Symposium 346 - Poster Abstracts


Close massive binary stars, BH mergers, and BH spins

Bogomazov, Alexey

Recently discovered bursts of gravitational waves provides a good opportunity to verify the current view on the evolution of close binary stars. Modern population synthesis codes help to study this evolution from two main sequence stars up to the formation of two final remnant degenerate dwarfs, neutron stars or black holes. To study the evolution of predecessors of BH mergers we use the "Scenario Machine" code. The scenario modeling allowed to describe the evolution of systems for which the final stage is a massive BH+BH merger. Our calculations show the plausibility of modern evolutionary scenarios for binary stars and the population synthesis modeling based on it. We discuss a possible values of spins of BH mergers, and give arguments in favour of different values of BH spins in BH mergers (low spin + low spin, high spin + high spin, low spin + high spin, etc).

High-mass X-ray Binaries: Evolutionary Population Synthesis Modeling

Zuo, Zhao-Yu

Using an evolutionary population synthesis code, we modeled the universal, featureless X-ray luminosity function of high-mass X-ray binaries (HMXBs) in star-forming galaxies. We put constraints on natal kicks and super-Eddington accretion factor, and presented the detail properties of modeled HMXBs, which may be investigated further by future high-resolution X-ray and optical observations.

Constraints from luminosity-displacement correlation of high-mass X-ray binaries

Zuo, Zhao-Yu

We have modeled the luminosity-displacement correlation of high-mass X-ray binaries with an evolutionary population synthesis code. Detailed properties including offsets of simulated HMXBs are presented under both common envelope prescriptions usually adopted, i.e., the αCE formalism and the γ algorithm. We suggest that the distinct observational properties may be used as potential evidence to discriminate between these two types of models.

V1187 Herculis, A Red Novae Progenitor, the Most Extreme Mass Ratio Solar-Type Binary

Samec, Ronald

Many solar type binaries have been found to undergo continuously decreasing orbital periods, presumably due to magnetic braking. A binary undergoing such a process will slowly coalesce over time as it loses angular momentum. This is due to ion winds streaming radially outward on stiff magnetic field lines rotating with the binary. Recently, overcontact binaries with decaying periods have been found to undergo a catastrophic merger (a Red Novae, RN). This leads to the formation of a single, fast rotating, spectroscopically, earlier-type star. As a part of the evolution of the RN progenitor, the binary’s mass ratio becomes more extreme and the Roche-lobe fill-out increases. It is believed that there is a maximum mass ratio leading to an instability and the occurrence of the RN. V1187 Her is apparently such a binary, and a progenitor of an RN. Complete BVRI photometric observations of V1187 Her were taken in May 2017 at Dark Sky Observatory in North Carolina with the 0.81-m reflector of Appalachian State University. Earlier, spectra were taken at Dominion Astrophysical Observatory with the 1.8m telescope. The spectral type is found to be F8±1V (6250 K) so the binary is of solar-type. V1187 Her was previously identified as a low amplitude (δV < 0.2 mag), short period, overcontact eclipsing binary (EW) with a period of 0.310726 d. Strikingly, despite its low amplitude, the early light curves show a total eclipse (eclipse duration: 31.5 minutes), which is a characteristic of an extreme mass ratio binary. A period study covering 11-years reveals a continuous period decrease (dP/dt= -4.7 X10-09 d/yr). The simultaneous W-D synthetic light curve solution gives a Roche Lobe fill-out of 79% along with a mass ratio of only 0.0440 ±0.0001. It has a cool spot region and its secondary component which is some 400 K hotter than the primary. The inclination is only 66.85±0.05˚ despite its total eclipses.

Analysis of spectrum variations in Hercules X-1 in terms of the accretion flow

Leahy, Denis

Hercules X-1 was observed extensively by the Rossi X-ray Timing Explorer (RXTE) over its 17 year lifetime. Here, the RXTE/PCA spectrum observations over the full 35 day cycle are analyzed. The spectral variations over 35-day phase are characterized and seen to have a regular behaviour. The changes are interpreted in terms of the precessing accretion disk. The most important variation is caused by the changing illumination of the inner edge of the disk, but other variations with different causes are also seen.

Optical properties of the black hole:shadow

Atamurotov, Farruh

The shape of the silhouette (shadow) can be used to test the corresponding theory of gravity for describing physical processes in the vicinity of a supermassive black hole. We have investigated how the size and apparent shape of the black hole is distorted due to the black hole’s parameters by analyzing unstable circular orbits, i.e.,. We adopted two observables, the radius Rs and the distortion parameter δs, characterizing the apparent shape; we found that the shape of the shadow is affected by the value of the rotation parameter and so on. The motion of photons around axially symmetric rotating black hole were considered with different parameters of the black hole.

Recent Observations of Newly Coalesced Solar Type Contact Binaries (Shallow Contact Systems) CW Scl, V530 And, NSVS 5066754, DD Indi

Samec, Ronald

Short period solar type binaries manifest strong magnetic activity and X-rays. Winds flow outward along field lines carrying both mass and angular momentum away from the binary. This process causes orbital decay, one result being a semidetached or marginally detached to shallow contact binary transition. Another process that can operate about critical contact is thermal relaxation oscillations. This a cyclic process whereby the binary goes from a marginal detached state to a marginal contact state and back until firm contact is attained. Recent precision BVRI CCD observations were undertaken of four systems in a state of marginal contact. In these studies the light curves were simultaneously solved with the Wilson-Devinney Code (WD) and period studies were undertaken of each. CW Sculptoris (T~ 6000K) was observed at Cerro Tololo InterAmerican Observatory (CTIO) with the 0.6-m SARA South reflector. An increasing period was determined from all available times of minimum light with a 1.14 ±0.16 X10-10 E2 quadratic term. Its mass ratio is~0.39, and the component temperature difference was 200 K. The Roche Lobe fill-out is only 7%. The inclination is 86˚. An eclipse duration of 19.5 minutes was determined for the primary eclipse, making the solution firmly determined. V530 Andromedae was observed at Dark Sky Observatory (DSO) 0.81-m reflector of Appalachian State University. Our present curves reveal that V530 And as a totally eclipsing, shallow contact binary. As with CW Scl, the period study (over a 14 year interval) showed a decreasing period. The component temperatures were 6750 and 6030 K large for a contact binary. The fill-out, however, is a mere 5%. The mass ratio was found to be 0.39. Two magnetic star spots, were determined. NSVS 5066754 (T1~5750 K) and DD Indus was (T1 ~ 5750K) will also be presented. Conclusions will be drawn following the summarized results.

The Role of Magnetic Field in State Transitions of BHXBs

Wang, Ding-Xiong

The role of magnetic field in state transitions of black hole X-ray binaries (BHXBs) is roughly described, and the following issues are discussed: (i) Why does each outburst of BHXBs always start from low/hard state (LHS), tracing an anti clockwise path in HID? (ii) Why are Episodic relativistic jets associated with intermediate state (IMS)? (iii) Does jet power correlate with black-hole spin? (iv) Why are steady jets associated with LHS, while disk winds appear in high/soft state (HSS)? It turns out that magnetic field can be regarded as the‘second parameter’ determining state transitions of BHXBs.


Samec, Ronald

A statistical study was begun with a poster session at the 2015 IAU GA--a compendium of more than 75 solar-type binaries was presented--each with a clearly decreasing orbital period. We conclude this study here by presenting new recently analyzed binaries to the previous study bringing the total to ~150 systems. These give strong evidence for the magnetic braking scenario regularly proposed by the binary community. Solar type binaries have strong magnetic activity and are X-ray sources. It is believed that binaries (for those of solar type), begin their existence as well detached fast spinning stars in groups that undergo gravitational interactions which leave them as binaries with several day periods. Since they are highly magnetic in nature, due to their convective envelopes and fast rotation, they undergo magnetic braking as plasma winds stream away from the stars on stiff rotating dipole fields. This action torques the binary, eventually bringing them into contact. They continue to coalesce and finally merge and undergo a cataclysmic event called a red nova, the aftermath of which is a single, earlier spectral type star (usually F or A). An age is computed for each binary, δt, based on the difference in the current orbital period and the proposed initial period, δP and the rate of orbital decay, dP/dt, δt= -δP/(dP/dt). The result is that the evolution of solar type binaries from formation to the present configuration averages more than two magnitudes faster than theory suggests. Further implications are explored.


de Freitas, Daniel Brito

We analyze the data from the 4 gravitational waves signals detected by LIGO through the lens of multifractal formalism using the MFDMA method, as well as shuffled and surrogate procedures. We examine the capability and robustness of this method to detect structural signatures made by different physical origins potentially present in gravitational waves. The quadratic form of multifractality spectrum demonstrates entire gravitational waves signal detected by LIGO have essentially multifractal nature and the source of this multifractality is mainly devoted to strong correlation which is another universality of these gravitational waves. However, an anomalous behavior occurs with the multifractal origin when the signal is divided into two regimes defined by the time where the variation in left side diversity takes a jump. We identified two regimes of multifractality in the strain measure of the time series by examining long memory and the presence of nonlinearities. The moment used to divide the series into two parts separates these two regimes and can be interpreted as the moment of collision between the black holes. Our main result is an empirical relationship between the variation in left side diversity and the chirp mass of each event, denoting that chirp mass is correlated to multifractal structure of gravitational wave time series. This empirical relation indicates that there exists a deterministic factor related to amount of stellar matter converted in energy when the coalescing supermassive binary black holes merger occurs.

Magnetically Active Noncontact Binaries: NSVS 2620909, NSVS 10083189, NSVS 10541123, GQ Cancri, FF Vulpecula

Samec, Ronald

Magnetic activity is common on solar type contact binaries and on the more massive RS CVn binaries. These exhibit magnetic spots, chromospheric activity (X-rays) and decreasing orbital periods due to magnetic braking. However, detached main sequence binaries should also should exhibit these characteristics since they are believed to be the progenitors of contact binaries. Recently observed detached binaries do indeed share these characteristics. Precision BVRI CCD observations were taken with the 0.81-m Dark Sky Observatory in North Carolina, and on the 1-m reflector at Kitt Peak National Observatory in 2013-2016. Analysis were done with the Wilson-Devinney (WD) program in noncontact (WD mode 2 or 4). FF Vulpecula has a period of 0.44 d. It is semidetached, i.e., with a V1010 Oph type configuration (larger component filling its critical lobe and the secondary under filing, mode 4). Thus, it is apparently approaching contact for the first time. The period is decreasing (dp/dt=-9.7×10-8d/yr). An equatorial hot spot was modeled on the cooler, secondary star, probably magnetic in origin. The component temperature difference, δt>1500 K. The solution confirms a total eclipse of 23 minutes duration. As expected, there is a magnetic cool spot region. NSVS 10541123 has a period of 0.59544 d. A quadratic ephemeris was determined, giving dp/dt= -5.96×10-7d/yr. The rapid period decline may indicate that the binary is undergoing magnetic braking and is approaching a contact configuration. It has a mass ratio of 0.5828, and a component δt of 2350 K. The large component difference confirms that the binary is not in contact. An apparent stream spot was computed with the primary component being the gainer. The fill-out is 96.3% for the primary component and 95.0% for the secondary component. The inclination is ~79˚. NSVS 10083189, GQ Cancri and NSVS 2620909 will also be highlighted. Conclusions are drawn following the significant results.

Overshooting beyond the convective cores of massive stars

Li, Yan

During the main sequence phase, massive stars develop central convective cores due to the central hydrogen burning. The development of convection is crucial for the evolution of massive stars, since it can bring hydrogen into the stellar center to be burnt. Overshooting beyond the convective core is then an important effect, as it can significantly enlarge the supply of nuclear fuel. On the other hand, the convective core usually becomes smaller and smaller during the main sequence evolution, leaving a chemical gradient region beyond the convective core. The semi-convection is assumed to develop in such a chemical gradient region, resulting in complicated partial mixing to modify the chemical profile that is crucial for the post-main-sequence evolution of massive stars. We investigated the overshooting mixing beyond the convective core by use of the k-omega model of Li (2012) for massive stars. We found that the convective core is considerably enlarged by about 0.15Hp, which is in agreement with results of other works in the literature. In addition, we also found an additional convection shell in the chemical gradient zone, where the semi-convection is usually assumed to develop. We noticed that the inclusion of the core overshooting significantly increases the separation between the convective core and the convection shell, making the convection shell quite thin and situated around the outer edge of the chemical gradient region. This effect entirely suppresses the semi-convective mixing predicted previously just above the convective core. As a result, the semi-convection can only be present near the outer edge of the chemical gradient zone, and result in a quite limited mixing effect on the chemical profile.

On the nature of the X-ray outbursts in Be/X-ray binaries

Yan, Jingzhi

Be/X-ray binaries are a major subclass of high mass X-ray binaries. Two different X-ray outbursts are displayed in the X-ray lightcurves of such systems. It is general believed that the X-ray outbursts are connected with the neutron star periastron passage of the circumstellar disk around the Be star. The optical emission of the Be star should be very important to understand the X-ray emission of the compact object. We have monitored several Be/X-ray binaries photometrically and spectroscopically in optical. The relationship between the optical emission and X-ray activities are found, which is very useful to explain the X-ray outbursts in Be/X-ray binaries.

X-ray binary Beta Lyrae and its donor component structure

Skulskyy, Mykhaylo

We propose an explanation of the steady state of X-rays of the massive interacting Beta Lyrae system – about 3 ?? for a donor and 13 ?? for an accretor. It was based on our spectral observations that led, in particular, to the study of the donor's magnetic field and the dynamics of developed circumstellar structures. Based on the analysis of magnetic field curves, curves of intensities and radial velocities of spectral lines with orbital phase we show that the mass transfer structure is having place due to the presence of a specific configuration of a magnetic donor field. The energy effect of a collision with the disk of a magnetized plasma increases greatly due to a rapid counter rotation of the disk rim towards the falling gas. As a result of such collisions, a significant heating of the disk side facing the donor is observed and the gas scattering shell is generated, which partially masks the components of this binary system outside of the Lyman limit and completely masks them in the soft X-ray region. This X-ray radiation is associated with Thomson scattering in a stellar wind and circumstellar jet-like structures.        Considering Beta Lyrae as a system that is finishing an active phase of the first mass transfer and its donor fills a Roche lobe, we have calculated the inner structure of such star preceding a forming of massive degenerate dwarf. We have applied the two-phase model in which core of the donor is isothermal and degenerated and outer envelope is described with politropic equation of state with index range of 4.9 - 4.95. Angular velocity is assumed to be constant. By integrating the the equilibrium equation we have obtained the macroscopic characteristics of the degenerate core –  its mass and radius, as well as size of the outer envelope. Also, we have solved the inverse problem – the parameters of the core have been found, namely, a parameter of relativism in the stellar center, a parameter of chemical composition and a central temperature.

The analogy of the K-correction in the topic of gamma-ray bursts

Borvák, Levente

It is well-known that there are two types of gamma-ray bursts (GRBs): short/hard and long/soft ones, respectively. The long GRBs are coupled to supernovae, but the short ones are associated with macronovae (also known as kilonovae), which can also serve as the sources of gravitational waves. Kilonovae occur during the merging of two neutron-stars. The neutron stars can be substituted by more massive black holes as well. Therefore, the topic of gamma-ray bursts (mainly that of short ones) and the topic of massive binaries, are strongly connected. In this contribution, the redshifts of GRBs are studied. The surprising result - namely that the apparently fainter GRBs can be, on average, at smaller distances - is discussed. In essence, the results of Mészáros et al. (2011, A&A, 529, A55) are verified using the newest samples of GRBs.

Emission-line diagnostics of nearby HII regions including interacting binary populations

Xiao, Lin

The evolution of binary-star systems vary from that of single stars as they can interact with their companions. This leads to mass loss, mass gain, or stellar mergers. We now know that most massive stars are binary stars interact with a binary companion (Sana et al., 2012, 2014). Therefore, in observed stellar populations their properties will be largely determined by past and ongoing binary interactions. We modelled nebular emission from young HII regions in great detail by combining the Binary Population and Spectral Synthesis (BPASS) code with the photoionization code cloudy (Ferland et al., 1998, 2013). We have compared these models to two different samples of observed HII region samples. We found that binary interactions must be considered as they can provide harder ionizing photons at later population ages beyond 10 Myr. These harder photons arise due to the production of less-massive helium stars which are not possible from single-star populations. These are the stars that go on to explode as type Ibc CCSNe. The existence of stellar populations with these helium stars means that we must reexamine the emission line diagnostics of HII regions. We currently have not include the accretion luminosity from X-ray binaries in our model populations since accretion physics is beyond the scope of our models. This can be significant at lower metallicities as the typical black hole mass in our populations increases; therefore our predictions for ionizing fluxes should be considered as a lower bound without this included. While accretion events are short lived, they are also extremely luminous and so may have an appreciable effect on the integrated spectrum of a stellar population in any given time bin. We would thus expect that once an accurate model of accretion onto compact remnants is included there will be an extra source of hard ionizing radiation within our models.

Discovery of a new ULX pulsar in NGC 300

Maitra, Chandreyee

We report the discovery of pulsations from NGC 300 ULX1 during simultanous XMM-Newton / NuSTAR observations in Dec. 2016. The period decreased from 31.7 s to 31.5 s over ~310 ks linearly, resulting in a spin period derivative of -5.6e-07 s/s, probably the largest ever observed. Archival Swift observations revealed that the period decreased exponentially from ~45 s to ~20 s over 21 months. The pulses are highly modulated with a pulsed fraction strongly increasing with energy and reaching nearly 80% at energies above 10 keV. The X-ray spectra can be modelled by a power law plus soft black-body component. In 2016 the X-ray luminosity was at ~3e39 erg/s. The X-ray spectra from an archival XMM-Newton observation from 2010 can be explained by the same model, however, with much higher absorption. This suggests, that the intrinsic luminosity did not change much since that epoch. NGC 300 ULX1 shares many properties with supergiant high mass X-ray binaries, however, at an extreme accretion rate.

On the long-term variability of high massive X-ray binary Cyg X-1

Karitskaya, Eugenia

We present the results of our study of spectral and photometric long-term Cyg X-1 variability on the base of the 44-year long series of multicolor photometric and many-year-long spectral observations. In 2006 it was revealed for the first time that the temperature of the optical component (О9.7Iab supergiant) was decreasing and its size was increasing over 7 years (1997–2003). The photometry performed at the Crimean Station of Sternberg Astronomical Institute (Lomonosov Moscow State University) shows that the variability of the supergiant in this system on the time scale of decades continues up to now - the mean level of star brightness continues to decrease since 1999 with the variations on smaller time scales superimposed. A remarkable very blue flare 2009 in U-band coinciding with X-ray flare is revealed. Our spectral observations show variations of HeI λ4713Å absorption line depths. There is a connection between X-ray and optical changes. The chaotic variations of X-ray flux sometimes reaching to "hard" - "soft" state irregular changes switch on when U brightness and HeI λ4713Å absorption line depth decrease. And inversely - they switch off during U brightness and HeI λ4713Å absorption line depth increasing. This is may be connected with star size variations, causing outflow gas instability. It is concluded that the fundamental parameters of the supergiant in the system of Cyg X-1 continue to vary.

The timing properties of black hole transient MAXI J1535-571 during its 2017 outburst from HXMT observations

QU, Jinlu

We study the state evolution and QPO properties of the new black hole candidate MAXI J1535-571 duringits 2017 outburst from Insight-HXMT observations from 2017 September 6 to 23 .  The results show that the source exhibits state transition from low hard state to hard intermediate state and the QPO phenomena. The  energy dependence and time lags of the QPOs up to 100 keV are studied. The source is similar to typical BHT GX 339-4.

The Insight-HXMT observation of the newly discovered transient X-ray pulsar Swift J0243.6+6124


Since the discovery of the Be/X-ray binary Swift J0243.6+6124 in an outburst showing up around 2017 October 3, Insight-HXMT has continuously monitored on this source in a broad energy band covering roughly 1-250 keV. With these observations the orbital ephemeris of the system are derived and refined later on, according to the variability of the spin frequency, which denotes a canonical Doppler effect endorsed by the orbital motion in a NS binary system. We therefore estimate the orbital ephemeris of Swift 0243.6+6124, thanks to the long term observations from Insight-HXMT. The orbital parameters are then obtained by us with a period around 27.35 days, a semi-major axis around 199 light-seconds, an eccentricity around 0.0842. We find from Insight-HXMT data that, both the pulse profile and phase-resolved spectrum evolve strongly with luminosity, which points to the complexity of the outburst exhibited by Swift J0243.6+6124.

Aperiodic variability in pulsars and the dynamo frequency

Mönkkönen, Juhani

Highly magnetized neutron stars accreting matter via an accretion disk offer a unique way to examine the interaction of plasma with the ultra-strong magnetic field. The magnetic field will truncate the disk at the so-called magnetospheric radius, inside which the disk matter is guided onto the neutron star surface where its energy is released in X-rays (so-called X-ray pulsars). The properties of the fast flux variability carry an imprint of the geometrical and physical conditions of the system.In the current work, we conducted comparative timing analysis of several X-ray pulsars whose magnetic fields are known through cyclotron line measurements. We examined the evolution of their power density spectra with respect to luminosity during outbursts. Our focus was on the power-law break frequency which in the perturbation propagation model (Lyubarskii 1997) is related to the inner radius of the accretion disk (Revnivtsev et al. 2009). Magnetic dynamo action occurs in all modern accretion disk simulations and its timescale can be linked to the growth of perturbations in the disk (Hogg & Reynolds 2016). Following the latest extension of the model (e.g. Mushtukov et al. 2018), the break frequency is expected to occur at the dynamo frequency of the inner disk radius. We now present limiting values for the ratio of the dynamo frequency to the Keplerian frequency of the inner radius. 

The role of metallicity in high mass X-ray binaries

Artale, Maria Celeste

In the last decade, different observational and theoretical studies indicate that the number and X-ray luminosity of high mass X-ray binaries (HMXBs) are directly correlated with stellar metallicity. Previous work claims that metal-poor progenitors are more likely to produce brighter HMXBs.  In this work, we test this correlation with metallicity by using population synthesis models and exploring the mechanisms that may produce this dependence.  We also investigate the HMXBs population in galaxies by implementing the results from population synthesis models into the galaxy catalogs from state-of-the-art galaxy formation models.

How Pulses in Short Gamma-Ray Bursts Constrain HMXRB Evolution

Hakkila, Jon

We present evidence that pulses in Short gamma-ray bursts (GRBs) originate from collisions between relativistically-ejected shells and slower-moving media (external shocks) rather than from collisions between shells of relativistically-ejected material (internal shocks). Using GRB/GW 170817A as a canonical example of a dying HMXRB system, we discuss how GRB pulse characteristics constrain the kinematics and structures of shocked regions produced in merging neutron star systems.

Massive stars as progenitors of merging black hole binaries

Giacobbo, Nicola

The recent detection of gravitational waves has proven the existence of massive stellar black hole binaries (BHBs), but the formation channels of BHBs are still an open question. Population-synthesis codes are one of the most powerful tools to investigate the origin of BHBs. In this talk, I describe my new code MOBSE, which is an updated version of the widely used binary population synthesis code, BSE (Hurley et al. 2002). In MOBSE, I have included the most recent models of star evolution,  wind mass-loss and core-collapse supernovae, which are the key ingredients to determine the fate of massive stars. Based on the results of MOBSE, I show that only massive metal-poor stars (Z < 0.002) can be the progenitors of gravitational-wave events like GW150914. Finally, I show that most of the binary systems leading to the formation of BHBs pass through the common envelope phase and through a high-mass X-ray binary phase.

Timing and Spectral studies of SXP 15.3 near its Eddington luminosity

Maitra, Chandreyee

SXP 15.3 (RX J0052.1-7319) is a Be X-ray binary pulsar located in the Small Magellanic Cloud. The source was classified as a transient X-ray binary candidate based on ROSAT observations in the 1990's, and pulsations at ~15.3 s were subsequently discovered from an outburst in 1996 from the ROSAT data. The source has never been studied in an outburst or a bright state ever since. Following reports of an outburst in November 2017, we triggered a Target of Opportunity observation of SXP 15.3 with AstroSat. We report here the first broadband spectral and timing studies of the source, when the source was accreting near the Eddington limit of 10^38 erg/s.  We discuss the energy dependence of the pulse profiles and the broadband spectrum in context of accretion onto magnetized neutron stars accreting near its Eddington limit.

Hot star winds over evolutionary timescales: revisions of the mass-loss prescription and impact of magnetic confinement

Keszthelyi, Zsolt

Surface phenomena, such as mass loss, angular momentum loss, and magnetism of the individual components of high-mass X-ray binary systems have a large impact on the evolution of these objects. Stellar evolution models rely on parametric prescriptions to account for such surface effects, however the evaluation, revision, and a change in currently-used prescriptions has become inevitable. In this contribution, we will present how the revision of mass-loss rates and the incorporation of surface magnetic fields can change modern stellar evolution models of massive stars.Mass-loss rates of hot stars are uncertain by at least a factor of two. Their dependence on surface properties, such as the effective temperature, may show abrupt changes at certain critical values. New theoretical results support observational indications that the effective temperatures at which these changes may occur had previously been overpredicted. These revised predictions urgently need to be adopted in stellar evolution models in view of their important consequences for massive star evolution.Magnetic confinement in hot, massive stars has far-reaching consequences. The effects arise from the magnetic field’s interaction with the stellar wind, leading to mass-loss quenching and magnetic braking. State-of-the-art stellar evolution models predict that magnetic progenitors can account for the formation of ‘heavy’ stellar mass black holes (such as those detected by the Advanced LIGO) and pair-instability supernovae, even at solar metallicity. 

Compact object mergers driven by gas fallback

Tagawa, Hiromichi

Recently several gravitational wave detections have shown evidence for compact object mergers. However, the astrophysical origin of merging binaries is not well understood. Further, there is a problem that existing astrophysical models for neutron star mergers typically predict a lower merger rate than observed. To solve the problem, we have proposed a new channel for mergers of compact object binaries. We examine the binary evolution following gas expansion due to a weak failed supernova explosion, neutrino mass loss, core disturbance, or envelope instability. In such situations the binary is possibly hardened by ambient gas. We investigate the evolution of the binary system after a shock has propagated by performing N-body/smoothed particle hydrodynamics simulations. We find that significant binary hardening occurs when the gas mass bound to the binary exceeds that of the compact objects. This mechanism represents a new possibility for the pathway to mergers for gravitational wave events. 

Prospecting the wind properties of IGR J16320-4751 with XMM-Newton and Swift

García, Federico

We present the results of a detailed study of the spectral evolution of the obscured NS-HMXB IGR J16320-4751 based on an orbital monitoring performed by XMM-Newton and Swift/BAT. By means of the hard X-ray data from Swift/BAT we re-calculated the ephemeris of the source, updating its reported orbital period. Based on the temporal evolution of the source revealed by the light-curves of each observation performed by XMM-Newton, we generated time-resolved spectra that we fitted using an absorbed comptonization and gaussian Fe Ka, XXV and Kß emission lines. We found that the spectral evolution is mainly governed by variations in the absorption column density, associated to the position of the NS along its orbit. Finally, assuming a typical wind profile for the supergiant star we simultaneously model the evolution of the hard X-ray light curve and the observed absorption column to constrain the eccentricity and inclination of the binary system, helping to better understand the behavior of these obscured sources.

Accretion Simulations of Eta Carinae and Implications to Massive Binaries

Kashi, Amit

We present high resolution numerical simulations of the colliding wind system Eta Carinae, showing accretion onto the secondary star close to periastron passage. This question was unanswered for more than a decade and our new high resolution simulations were able to finally provide an answer. We find that the smooth stellar winds collide and develop instabilities, mainly the non-linear thin shell instability, and form filaments and clumps. We find that a few days before periastron passage the dense filaments and clumps flow towards the secondary as a result of its gravitational attraction, and reach the zone where we inject the secondary wind. We run our simulations for the conventional stellar masses, M1=120 Msun and M2=30 Msun, and for a high mass model, M1=170 Msun and M2=80 Msun, that was proposed to better fit the history of giant eruptions in the nineteenth century. As expected, the simulations results show that the accretion processes is more pronounced for a more massive secondary star. We obtain orbital parameters of the binary system from the simulation results, and learn about the recovery of Eta Carinae from its giant eruptions. This leads us to the conclusion that the presence of a binary companions can have a huge influence on the evolution of massive star, especially at later stages where it may undergo giant episodes of mass loss.


Yankova, Krasimira

The aim is to study the extension on advective hypothesis in the general relativity. As well to trace the prerequisites and consequences in the space-time metrics from excitation and action of the non-deforming advection. This mechanism is proposed to the unified the model  high-energy state at accretion in the AGN and non-ACTIVE(sleeping) galactic nucleusses and micro-quasars for completeness. Such type advection is related the occurrence of the connections between the elements in quasar; and for that allows to research the evolution of the mechanism in some of them due to the development of these intercomponent connections.

Modelling the viscous decretion discs of Be/X-ray binaries

Brown, Rory

Be/X-ray binaries are the largest observable population of HMXBs, making them a valuable tool for probing the physics of binary systems and compact objects. Even though there are well over 100 Be/neutron star binaries, there is only one confirmed Be/black hole binary. Previous theoretical work suggests this is not due to their formation but due to differences in X-ray luminosity. We use Smoothed Particle Hydrodynamics simulations to explore the differences between binaries with compact objects of varying mass. It is evident from these models that Be/X-ray binaries with black hole companions are harder to observe. These simulations are also applied to a specific case in Be/neutron star binaries, where the neutron star plunges directly through the disc, that leads to uncommon observational behaviours.

An insight into the low level accretion in Be/X-ray transients

Rouco Escorial, Alicia

I will present the results of several Be/X-ray transients (i.e., GRO J1750-237, 4U 0115+63, GRO J1008-57, GX 304-1, KS 1947+300) after the end of their outbursts when the sources are thought to transit to quiescence. Our monitoring campaigns are focused on studying low-level accretion processes onto the magnetized neutron stars (1x1012-1x1013 G) present in these systems. We find that some sources decay directly to quiescence, a few systems settle in a decaying low luminosity state during which very short (timescales of only a few days) enhanced accretion episodes occur, while several other systems always stay in an intermediate accretion-rate level with X-ray luminosities of 1034-1035 erg/s and never appear to reach quiescence. I will discuss these results in the context of physical processes that could produce the observed phenomena, such as low-level direct accretion onto the neutron star (e.g., due to leakage of matter to the surface or accretion through a cold disk), accretion down to the magnetospheric boundary, or emission associated with the propeller effect that might be active in some systems.

Optical counterparts of two ultraluminous X-ray sources NGC4559 X-10 and NGC4395 ULX-1

Vinokurov, Aleksandr

We study the optical counterparts of ultraluminous X-ray sources NGC 4559 X-10 and NGC 4395 ULX-1. Their absolute magnitudes, after taking the reddening into account, are MV ≈ −5.3 and MV ≈ −6.2, respectively. The spectral energy distribution of the NGC 4559 X-10 counterpart is well fitted by a spectrum of an A-type star, whereas NGC 4395 ULX-1 has a blue power-law spectrum. Optical spectroscopy of NGC 4395 ULX-1 has shown a broad HeII λ4686 emission, which puts this object in line with all the other spectrally-studied ULXs. Analyzing the absolute magnitudes of 16 well-studied ULX counterparts we find that the intrinsically fainter counterparts with MV > −5.5 have on average black body like or power law spectral energy distributions. In other ULX counterparts with MV < −5.5 we may observe a power law like SED, the only one donor is in NGC 7793 P-13 (the ULX-pulsar). One may suggest that as the original accretion rate decreases (but nevertheless remains supercritical), the optical luminosity of the wind becomes lower and the donor star might dominate. Using the Swift archival X-ray data for NGC 4395 ULX-1, we have found a period of 62.8 ± 2.3 days. The X-ray phase curve of the source is very similar to the precession curve of SS 433.

Probing superorbital variations in SMC X-1 with Suzaku through simultaneous timing and spectral analysis

Pradhan, Pragati

SMC X-1 was observed with Suzaku ten times during different intensity states of the superorbital variation in 2011. We present a broadband (0.3-70 keV)spectral analysis and a detailed joint comparison of the spectra in these intensity states for the first time and interpret the results to map accretion geometry/mechanisms. The spectrum in all the states can be described by an absorbed powerlaw with a smoothened high energy cutoff. Additional black-body component and Fe K emission line is detected, apart from few other low energy emission lines. The spectral shape is also dependent on flux with the hard X-ray spectrum steepening with increasing flux. Through spectral analysis, we probe the nature of the absorber in the precessing warp of SMC X-1 that cause the superorbital modulation. We have carried out orbital corrections for Doppler shift in the HXD lightcurves and report detection of pulsations in hard X-rays in all but one observation. Detection of the X-ray pulses in the low state help us limit the contribution of the scattering/reprocessed component of the X-ray emission in the low state.

Multitude of iron lines in OAO 1657-415 detected with Chandra

Pradhan, Pragati

We present a high resolution X-ray spectrum of the accreting X-ray pulsar, OAO 1657-415 with HETG onboard Chandra, revealing the presence of a broad line component at 6.3 keV in addition to the neutral iron K α line at 6.4 keV. This is interpretated as Compton shoulder arising from the Compton scattering of the 6.4 keV flourecense photons making OAO 1657-415 the second accreting neutron star where such a feature is detected. A Compton shoulder reveals the presence of dense matter surrounding the X-ray source. We did not detect any periodicity in the lightcurve and obtained an upper limit of ∼ 2% for the pulse fraction during this observation. This could be due to the smearing of the pulses when X-ray photons are scattered from a large region around the neutron star. In addition to the K α , Fe K β and Ni K α lines already reported for this source, for the first time, we also report the presence of Helium and Hydrogen-like iron emission lines at 6.63, 6.7 and 6.97 keV in the HETG spectrum. The detection of such ionized lines are rare in X-ray binaries and shows very high ionisation parameter in the surrounding medium.

Gravitational wave signal from neutron star mergers as a tool to constrain EOS for nuclear matter

Zakharov, Alexander

Gravitational wave signal from the neutron star merger has been detected recently. We present a set of gravitational wave templates which are calculated with different choices of equation of state (EOS) for neutron stars. We discuss opportunities to rule out or/ and constrain some EOS from future observations of gravitational wave signals and their electromagnetic counterparts.

The Formation of Spectroscopic Massive Binaries via Early Disk Fragmentation and Migration

Kuiper, Rolf

Accretion-driven luminosity outbursts are a vivid manifestation of variable mass accretion onto protostars. We present three-dimensional gravitation-radiation-hydrodynamics simulations of pre-stellar core collapse, star, and disk formation. We find that accretion disks of young massive stars violently fragment without preventing the (highly variable) accretion of gaseous clumps onto the protostars. This episodic accretion of clumps is accompanied by luminous outbursts. Furthermore, while acquiring the characteristics of a nascent low-mass companion, some disk fragments migrate toward the central massive protostar with dynamical properties showing that their final Keplerian orbits resemble that of a close massive binary system. We predict the fragmentation of massive circumstellar accretion disks as a viable road to the formation of spectroscopic massive binaries and the recently observed strong accretion bursts in high-mass star forming regions.

Clear anti-correlation between X-ray luminosity and pulsed fraction in the Small Magellanic Cloud pulsar SXP 1323

Yang, Jun

We report the anti-correlation between pulsed fraction (PF) and luminosity of the X-ray pulsar SXP 1323, found for the first time in a luminosity range \boldmath{$10^{35}$}--$10^{37}$ erg s$^{-1}$ from observations spanning 15 years. The phenomenon of a decrease in X-ray PF when the source flux increases has been observed in our pipeline analysis of other X-ray pulsars in the Small Magellanic Cloud (SMC). It is expected that the luminosity under a certain value decreases as the PF decreases due to the propeller effect. Above the propeller region, an anti-correlation between the PF and flux might occur either as a result of an increase in the un-pulsed component of the total emission or a decrease of the pulsed component. Additional modes of accretion may also be possible, such as spherical accretion and a change in emission geometry. At higher mass accretion rates, the accretion disk could also extend closer to the neutron star (NS) surface, where a reduced inner radius leads to hotter inner disk emission. We will discuss the implication of these modes and the beam configuration.

Rapid evolution of the SS 433 system with relativistic jets

Goranskij, Vitaly

The eclipsing system SS 433 (V1343 Aql) with moving emission lines in the spectrum consists of an A4-A8 giant (Gies et al., 2002) and a neutron star (Goranskij, 2013). The moving components of Balmer and He I lines are formed by a pair of oppositely directed, highly collimated and precessing relativistic jets of gas moving with a velocity of 0.26 c. The orbital period of 13.082 day, the jet precession period 162 days, and jet nodding period 6.28 day are present in both photometric and spectroscopic data. The star is located in the center of radio structure W50 interpreted as a 10000-year old supernova remnant. We present the results of forty-year monitoring, which includes multicolor photometry and synoptic observations analyzed along with fragmentary spectroscopic and radio data. Photometry shows secular trend towards decreasing amplitudes of all periodic variations by about 40 percent. We observed episodes of eclipse disappearance during several orbital periods. We explain such episodes as consequence of a sporadically forming common envelope, when Roche lobe of the neutron star is overfilled. Then gas flows in the circumbinary extended and precessing disk (earlier described by Barnes et al., 2002) through the Lagrangian point L2. We observed also episodes of blocking the jets by the common envelope, the explosive ejection of the common envelope, and recovery of the jets. These phenomena suggest that the mass transfer from the A-type companion passes into a dynamical timescale.

Ultraluminous X-ray sources

Fabrika, Sergei

The origin of ultraluminous X-ray sources (ULXs) in external galaxies whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times is mysterious. The X-ray spectra indicate a presence of hot winds in their accretion disks. The new results were discovered, ULX-pulsars and high-velocity outflows up to 0.2c. They are in accordance with the super-Eddington accretion. Here we analyze the variability properties of only five ULXs which show flat-topped noise (FTN) and QPO in their X-ray power density spectra. In each ULX the mass accretion rate may vary up to 3-4 times, and with decreasing the accretion rate (reduction the spherization radius), the hardness ratio and luminosity increase, FTN and QPO may dissapear. We may potentially measure the black hole masses using X-ray luminosities. However, the strongest evidences come from optical spectroscopy. The spectra of the ULX counterparts are very similar to that of SS433 and WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state. We find that the spectra do not originate from WNL/LBV type donors but from strong winds in the accretion disks, which have similar physical conditions as the stellar winds from these stars. The results suggest that the bona-fide ULXs have supercritical accretion disks.

Low-level accretion onto highly magnetized neutron stars

Tsygankov, Sergey

In my talk I will consider the case of transient highly magnetized neutron stars accreting in a broad range of rates,  focusing  on  their  behaviour  in  the  very  end  of  the  outbursts.  At  low  mass  accretion  rates  the centrifugal  inhibition of the accretion (aka  “propeller  effect”,  one  of  the  most  direct  evidence  of the  ultra-strong magnetic field presented in the vicinity of the neutron stars) was discovered in a few systems. I will review  observational  manifestations  of the propeller effect in X-ray pulsars with broad range of the magnetic fields from 108 to 1014 G with main focus on our recent discoveries. In the second part of my talk I will introduce a model explaining the existence in some X-ray pulsars of an unexpected quasi-stable state characterized by the accretion rate of ~1014-1015 g/s. We associate this state  with the accretion from cold (non-ionised) disc with temperature below ~6500 K. We argue that a transition to such accretion regime should be observed in all X-ray pulsars with certain combination of the rotation frequency and magnetic field strength.


Takahashi, Koh

Recent theory predicts that a first star is born with a massive initial mass of > ~100 Msun. Pair instability supernova (PISN) is a common fate for such a massive star. Our final goal is to prove the existence of PISN and thus the high mass nature of the initial mass function in the early universe by conducting abundance profiling, in which properties of a hypothetical first star is constrained by metal-poor star abundances. In order to determine reliable and useful abundances, we investigate the PISN nucleosynthesis taking both rotating and non-rotating progenitors for the first time. We show that the initial and CO core mass ranges for PISNe depend on the envelope structures: non-magnetic rotating models developing inflated envelopes have a lower-shifted CO mass range of ~ 70–125 Msun, while non-rotating and magnetic rotating models with deflated envelopes have a range of ~ 80–135 Msun. However, we find no significant difference in explosive yields from rotating and non-rotating progenitors, except for large nitrogen production in non- magnetic rotating models. Furthermore, we conduct the first systematic comparison between theoretical yields and a large sample of metal-poor star abundances. We find the predicted low [Na/Mg] ~ -1.5 and high [Ca/Mg] ~ 0.5–1.3 abundance ratios are the most important to discriminate PISN signatures from normal metal-poor star abundances, and confirm that no currently observed metal-poor star matches with the PISN abundance.

Analytical solution for magnetized thin accretion disk in comparison with numerical simulations

Cemeljic, Miljenko

A magnetic extension of hydrodynamical solution for a thin accretion disk around a central star is obtained by using the method of asymptotic approximation. For the first time we add the energy equation in the asymptotic approximation. We compare the analytical results with the long-lasting resistive and viscous MHD axi-symmetric numerical simulations of the quasi-stationary disk.

Gamma-ray Bursts: A Brief Survey of the Diversity

Meszaros, Attila

      The separation of the gamma-ray bursts (GRBs) into short/hard and long/soft subclasses, respectively, is well supported both theoretically and observationally. The long ones are coupled to supernovae type Ib/Ic - the short ones are connected to the merging of two neutron stars, where one or even both neutron stars can be substituted by black holes. These short GRBs - as merging binaries - can also serve as the sources of gravitation waves, and are observable as the recently detected macronovae.       Since 1998 there are several statistical studies suggesting the existence of more than two subgroups. There can be a subgroup having an intermediate durations; there can be a subgroup with extra long durations; the long/soft subgroup itself can be divided into two subclasses with respect to the luminosity of GRBs; etc. The authors with other collaborators provided several statistical studies in this topic. This topic of the GRB-diversity is shortly surveyed in this contribution.

Massive Star Mass-Loss Revealed by X-ray Observations of Young Supernovae


Massive stars lose a considerable amount of mass as they evolve through various phases during their lifetime. Despite years of observations and modelling, the amount of mass lost is still debated. When the star explodes as a supernova, the resulting supernova shock wave expands in the medium created by the stellar mass-loss. The resulting X-ray emission from the star, if it is thermal in origin (as it is about half the time), depends on the square of the density of the ambient medium. The density can be related to the mass-loss rate of the progenitor star. Thus, the X-ray emission can be used to probe the magnitude of the stellar mass-loss in the decades or centuries before the star's death. If the emission is non-thermal it can still set limits on the mass-loss rate. The X-ray lightcurve of the supernova can provide information regarding both the magnitude of the mass-loss as well as its evolution in time before core-collapse. In a few cases, detailed modelling can provide highly accurate results.We have aggregated together data available in the literature, or analysed by us, to compute the X-ray lightcurves of almost all young supernovae (SNe) that have been detected in X-rays. Currently we have about 60 SNe spanning all the various types, but the database is expanding rapidly. The lightcurves span 12 orders of magnitude in luminosity. We use this library of lightcurves and spectra to explore the mass-loss rates of massive stars that collapse to form supernovae, including red supergiants, Wolf-Rayet stars, binary, and unidentified progenitors. The mass-loss rates are lowest for the common Type IIP supernovae, but increase by several orders of magnitude for the highest luminosity X-ray supernovae. The highest mass-loss rates, and the mass-loss evolution, differ considerably from that predicted by stellar evolution models.  The range of mass-loss rates, and implications for the mass-loss from massive stars, will be discussed.

Significant roles of accretion rings in X-ray binaries

Inoue, Hajime

X-ray light curves of three X-ray pulsars, Her X-1, LMC X-4 and SMC X-1, folded with their respective super-orbital periods, are shown to be well reproduced by a model that X-rays from a compact object towards us are periodically obscured by a precessing ring at the outermost part of an accretion disk around the central object. A situation is considered that matter from a companion star flows into a gravitational field of a compact star and initially forms a circular ring around the compact star under a balance between the centrifugal force and the gravitational force.  A simple energetics-argument indicates that a precession of such a ring is possible to be excited.  From the best fir parameters of the model fit to the super-orbital light curves, we see that the optical depth of the accretion ring is commonly around unity for Compton scattering and that the ring should suffer from a significant effect of X-ray heating from the central X-ray source.  By considering why and how such an accretion ring is realized, the following evolution of the ring matter is suggested:  Matter from the companion star initially forms a geometrically thick ring and accumulates there until the optical depth becomes around unity.  Then, the matter in the thick ring gradually cools down under a balance between X-ray heating and radiative cooling, and shrinks to a geometrically thin ring at the cross section center of the ring.  Angular momenta of the rotating matter are effectively transferred from the inside to the outside in the thin ring and the inside matter finally falls through a geometrically thin accretion disk towards the central compact object.  This scenario on the outermost part of accretion disks can well explain several observational aspects of accreting X-ray binaries.

Time lag in transient HMXB, and other disk accreting sources

Bisnovatyi-Kogan, Gennagy

Model is developed for time lag between maxima of the source brightness in different wave-lengths, during a transient flash of luminosity, connected with a short period of increase of themass flux onto the central compact object. A simple formula is derived for finding the time delayamong events in different wavelengths, valid in general for all disk accreting cosmic sources. Inclose binaries with accretion disks the time lag is connected with effects of viscosity defining aradial motion of matter in the accretion disk.  The validityof these model is shown by comparison with observations of several galactic accretingsources.

Searching for young radio pulsars located in new SMC SNR candidates

van Jaarsveld, Johanna

The SMC went through relatively recent star formation episodes, producing a large number of O and B stars, many of which are companions in high mass X-ray binary systems.  A recent census by Haberl & Strum (2016) identified 120 HMXBs in the SMC - similar to the population in the Milky Way, despite the fact that the SMC is only one-fiftieth the mass, we therefore know that the SMC harbours many neutron stars and many interesting binaries.  However, despite this large population of neutron stars only five rotation powered pulsars have been discovered in the SMC through various Magellanic Cloud radio surveys.  To improve on the sensitivities achieved in the previous surveys, we conducted the deepest, most sensitive observations with the 20 cm Parkes Multi-Beam receiver of 6 new SNR candidates located in the SMC, aiming to find new radio pulsars, some of which could be progenitors to HMXBs or members of double neutron star binaries.   We will report on any newly discovered radio pulsars, and in the case of not detecting any radio emission, we will determine a reasonable luminosity limit by using the increase in sensitivity with respect to the previous surveys, which we can then compare with potential PWNe to constrain the neutron star properties.

X-ray reprocessing: Through the eclipse spectra of high and low mass X-ray binaries with XMM-NEWTON

Aftab, Nafisa

Study of X-ray reprocessing is one of the key diagnostic tool to probe the environment in X-ray binary systems. Difficult aspect to study X-ray reprocessing is the presence of primary radiation from the compact star along with the reprocessed radiation. Eclipsing X-ray binaries make an ideal condition to study reprocessed X-rays, as the X-rays detected during eclipse are purely reprocessed while the primary X-rays are blocked by the companion star. We carried out first comprehensive studies of X-ray reprocessing with a number of eclipsing High Mass X­-ray Binary and Low Mass X­-ray Binary (HMXB and LMXB) systems during and outside eclipse with XMM­-NEWTON EPIC pn. Comparing eclipse and out-of-eclipse spectra of these sources we have found ample diversity in the X-ray reprocessing characteristics in HMXBs, even in the same source at different epochs the variation is quite large. In spite of having much weaker wind environment, the flux ratio of out-of-eclipse to eclipse in LMXBs is in a range comparable to the HMXBs. The analysis shows very strong Iron ka emission line during eclipse phases in most of the HMXBs and week or no Iron emission lines in LMXBs. Equivalent width of Iron emission lines in Supergiant Fast X-ray Transients (SFXTs) are large during eclipse, similar to that in Supergiant HMXBs (SgHMXBs). There are some significant system to system differences. For example low equivalent width of Iron ka emission line in HMXB Cen X-3 during eclipse, very week Iron emission line in HMXB SMC X-1,  comparable out-of-eclipse to eclipse flux ratio in LMXB  AXJ 1745.6–2901 irrespective of intensity state etc. Overall we try to infer the wind and accretion disk characteristics, which are the reprocessing agents in the HMXB and LMXB systems respectively.

Circumstellar structures around high-mass X-ray binaries

Gvaramadze, Vasilii

Many high-mass X-ray binaries (HMXBs) are runaway systems, travelling through space with high velocities. Stellar wind and radiation of donor stars in HMXBs along with outflows and jets from accretors interact with the local interstellar medium and, under proper conditions, produce curious circumstellar structures. I will report the detection of several such structures and discuss their possible origin.

Models of Very High Energy Emission of X-rays Binaries: Numerical GRMHD Simulations of Magnetic Reconnection Events and Radiative Transfer/Particle Calculations.

Rodriguez-Ramirez, Juan Carlos

Leptonic and hadronic non-thermal processes have been considered to model the very high energy (VHE) component of the emission spectrum of X-ray binaries. However, the hadronic models are still poorly developed. In this work we consider particle acceleration produced by magnetic reconnection in the core region of accreting black holes (BH) to numerically calculate the resulting VHE emission produced due to hadronic and leptonic processes. We first perform general relativistic magnetohydrodynamical (GRMHD) simulations of BH accretion disks seeking for strong magnetic reconnection events, and chose the appropriate environment profiles for our emission calculations. We then perform leptonic radiative transfer calculations on the chosen background snaptshots in order to obtain the photon field that will be the target for photo-hadronic interactions. Then, we inject high energy protons (according to the characteristics of the plasma in the reconnection regions) and compute photon fluxes stemming from the interactions of the injected protons with the background photon and magnetic fields (using the CRPropa3 code). Finally, we obtain the resulting spectral energy distributions and discuss the characteristics of  their corresponding accretion disks sources and hosting X-ray binary systems.

Massive star evolution : mixing processes, rotationally-induced mass loss, and mass-luminosity relationships.

Higgins, Erin

Massive star evolution remains ambiguous with respect to key physical processes, yet advancements in theoretical modelling are essential in understanding the progenitors of black holes and neutron stars. As we continue searching for gravitational wave events like GW150914, it will be crucial to understand the evolutionary channels which led to such an event. We study the dominant processes such as mass loss, convective overshooting and rotation with the aim of constraining physical parameters qualitatively through MESA evolutionary models. Our results highlight the necessity of rotational mixing since observed intermediate level nitrogen enrichments are unachievable with only mass loss and convective overshooting, employed as mixing processes. We calibrate our stellar evolution models for a range of objects and compare them to previous grids of models (such as Brott et al. 2011, Ekstrom et al. 2012).

On the long-term evolution of cyclotron lines in accreting neutron stars

D'Aì, Antonino

In my presentation I'll focus on two important open issues in the physics of accreting magnetized neutron stars: how the accretion flow settling on their surface affects the local topology of the magnetic field lines and how the secular evolution of the binary system depends on the dissipation rate of the NS intrinsic magnetic field.In the X-ray spectra of accreting NS binaries, the presence of the cyclotron resonant scattering features,indicates the intensity of the field in the region where the line is formed. This optically thick region can move in correlation, or anti-correlation, with the mass accretion rate, depending if a radiative shock is formed or not. In this way, cyclotron features probe the B-field intensity along the accretion column and, for spectra selected at the same level of luminosity but at different epochs, the field's evolution on longer time-scales. I will report on recent spectroscopic studies on cyclotron line features obtained from the Swift/BAT survey data for a set of high-mass binaries and what new clues they give for the current understanding of magnetic fields in accreting neutron stars [1,2,3].references:[1] A. D'Aì, G. Cusumano, M.Del Santo, V.La Parola, A.Segreto, 2017, MNRAS, 470, 2457[2] G. Cusumano, V. La Parola, A. D'Aì, et al., 2016, MNRAS, 460, L99[3 ]V. La Parola, G. Cusumano, A.Segreto , A.D'Aì, 2016, MNRAS, 463, 18

Global Magnetohydrodynamic Simulations of Coexisting Hot and Cool Disks in Black Hole Candidates

Matsumoto, Ryoji

We present the results of global three-dimensional magnetohydrodynamic simulations of the hard-to-soft state transitions in Cyg X-1 and other black hole candidates. We apply a radiation magnetohydrodynamic code CANS+R which adopts HLLD+MP5 scheme to solve resistive magnetohydrodynamic equations, and M1-closure scheme to update the 0th and 1st moment equations of radiative transfer. This code can handle both optically thin and optically thick region. The initial state is a hot torus threaded by weak azimuthal magnetic fields. Radiative cooling terms are switched on after a quasi-steady disk is formed by efficient angular momentum transport by magnetic turbulence driven by the magneto-rotational instability (MRI). When the equatorial density of the torus exceeds the threshold for the onset of the cooling instability, the torus shrinks in the vertical direction by cooling. When the global azimuthal magnetic field is symmetric with respect to the equatorial plane, magnetic pressure becomes dominant as the disk shrinks in the vertical direction by cooling. When the disk near the black hole stays in an optically thin, hot state, the interaction between the strong magnetic fields in the outer disk and the quasi-periodically reversing dynamo magnetic fields in the inner hot disk drives magnetic reconnection and plasmoid ejections. Furthermore the additional heating by magnetic reconnection prevents the outer disk to complete the transition to an optically thick, standard disk. The coexisting inner hot disk and outer cool, strongly magnetized disk can explain the X-ray spectrum and X-ray time variabilities observed in Cyg X-1 and other black hole candidates. We also discuss the effects of the thermal conduction.

Modeling of the 35-day optical variations of HZ Her/Her X-1

Shakura, Nikolay

The photometric optical light curve of the X-ray binary Her X-1/HZ Her collected over more than 40 years of observations (including those of the authors) is analysed. The model 35-day light curve of the system is calculated and compared with observations. The model include a precessing warped accretion disk around a neutron star which freely precesses with the 35-day period. The precession of the disk is locked to the neutron star precession via dynamical interaction of gas streams forming the accretion disk. The X-ray diagram shape formed by the complex accretion structure around the neutron star magnetic poles is also taken into account for the calculation of the X-ray illumination of the optical star atmospher which shapes the observed optical light curves. The proposed model well describes the observed changes of the 35-day light curve with the precession period phase, which cannot be explained by the precession of the accretion disk only. 

Testing how massive stars evolve, loose mass, and collapse at low metal content

Rojas Montes, Eliceth Y.

In order to test massive star evolution above 25 Solar masses, we performspectral analysis on a sample of massive stars in the Small Magallenic Cloud that includes both O stars as well as more evolved Wolf-Rayet stars.We present a grid of non-LTE stellar atmospheres that has been calculatedusing the CMFGEN code, in order to have a systematic and homogeneous approach. We obtain stellar and wind parameters for O stars, spectral typesranging from O2 to O6, and the complete sample of known Wolf-Rayetstars. We discuss the evolutionary status of both the O and WR stars andthe links between them, as well as the most likely evolutionary pathtowards Black Hole formation in a low metallicity environment, includingtesting theoretical predictions for mass-loss rates at low metallicities.

Statistical study of magnetic reconnection in accretion disks systems around HMXBs

Kadowaki, Luis H.S.

Highly magnetized accretion disks are present in high-mass X-ray binaries (HMXBs). The complex emission observed in these systems indicates the presence of different regimes of accretion. A hot, low-density magnetized disk corona is frequently invoked in order to explain the non-thermal high-energy emission. A potential mechanism to explain the transition between the High/Soft and Low/Hard states observed in HMXBs can be attributed to fast magnetic reconnection induced in the turbulent corona. According to this model, the power released by fast reconnection between the magnetic field lines arising from the inner accretion disk and the lines anchored into the compact source could accelerate relativistic particles in a first-order Fermi process and produce the observed non-thermal emission. In this work, we present results of high-resolution three-dimensional local magnetohydrodynamic (MHD) simulations and global general-relativistic MHD (GRMHD) simulations of accretion disks around black holes that show that fast reconnection events, similar to those occurring in the solar corona, can naturally arise in the coronal region of magnetized accretion disks in presence of turbulence triggered by MHD instabilities, indicating that such events can be a potential mechanism to explain the transient non-thermal emission in HMXBs. To find the zones of fast reconnection, we have employed an algorithm to identify the presence of current sheets in the turbulent regions and computed statistically the magnetic reconnection rates in these locations obtaining average reconnection rates consistent with the predictions of the theory of turbulence-induced fast reconnection.

The formation of massive binaries as a result of the dynamical decay of trapezium systems

Allen, Christine

We study the dynamical evolution of 10 multiple systems of trapezium type with very massive components.  As initial conditions we take the planar positions, transverse velocities, distances and masses from the best observations found in the literature.  Radial velocities and z-positions are not available, but were modeled by Monte Carlo simulations.  Our results show that the dynamical lifetimes for these systems are extremely short, shorter than the evolutionary lifetimes of their massive components.  Only assuming much larger masses for the components both lifetimes become comparable.  These results are similar to the dynamical lifetimes we found previously for the minicluster associated with the B component of the Orion Trapezium and for the Orion Trapezium itself. The end result of the simulations is usually  a close massive binary, sometimes a triple system.

Properties of the Ultraluminous X-ray Source Populations in Chandra Source Catalog 2.0

Kovlakas, Konstantinos

The nature and evolution of ultraluminous X-ray sources (ULXs) is an open problem in astrophysics. They challenge our current understanding of stellar compact objects and accretion physics. Recent discoveries of ULX pulsars and reports of ULXs serving as sources of heating of the universe during the epoch of reionization, further demonstrate the importance of this intriguing and rare class of objects.In order to overcome the difficulties of directly studying the optical associations of ULXs, we generally resort in statistical studies of the stellar properties of their host galaxies.We present the largest scale such study based on the combination of Chandra archival data with the most complete galaxy catalogue of the local universe (D < 100 Mpc).This analysis incorporates robust distances and stellar population parameters (star formation rate, stellar mass, metallicity) based on associated multi-wavelength information. We explore the association of ULXs with galaxies in the (SFR, stellar mass, metallicity) space and we compare our results with predictions from X-ray binary population synthesis models.In addition, we discuss the effects of source confusion in large-volume studies of individual sources, and we present a statistical model to account for their clustering based on spatially resolved star-formation histories.

Two views of the massive binary population

McBride, Vanessa

Massive X-ray binaries are the progenitors for gravitational wave sources, but also tracers of star formation visible well outside the Milky Way. While well over a hundred massive X-ray binaries have been identified in the Milky Way, only a handful of radio pulsars with massive companions are known to exist. Such binaries harbouring young pulsars are expected to evolve into massive X-ray binaries. In this work, we attempt to quantify observational selection effects in the context of binary evolution models to understand these different manifestations of the same underlying population of massive binary stars.

3D Time-dependent Hydrodynamical and Radiative Transfer Modeling of Eta Carinae's Innermost Fossil Colliding Wind Structures

Madura, Thomas

Eta Carinae is the most massive active binary within 10,000 light-years. While famous for the largest non-terminal stellar explosion ever recorded, observations reveal a supermassive (120 M_Sun) binary consisting of a highly unstable LBV and either a WR or extreme O star in a very eccentric orbit (e = 0.9) with a 5.54-year period. Dramatic changes across multiple wavelengths are routinely observed as the stars move about in their highly elliptical orbits, especially around periastron when the hot (~40 kK) companion star delves deep into the denser and much cooler (~15 kK) extended wind photosphere of the primary. Many of these changes are due to a dynamic wind-wind collision region (WWCR) that forms between the stars, plus expanding radiation-illuminated fossil WWCRs formed one, two, and three 5.54-year orbital cycles ago. These fossil WWCRs have been spatially and spectrally resolved by the Hubble Space Telescope (HST)/STIS at multiple epochs, resulting in data cubes that spatially map Eta Carinae’s innermost WWCRs and follow temporal changes in several forbidden emission lines (e.g. [Fe III] 4659Å, [Fe II] 4815Å) across the 5.54-year cycle. We present initial results of 3D time-dependent hydrodynamical and radiative-transfer simulations of the Eta Carinae binary and its WWCRs with the goal of producing synthetic data cubes of forbidden emission lines for comparison to the available HST/STIS observations. Comparison of the theoretical models to the observations reveals important details about the binary’s orbital motion, photoionization properties, and recent (5 – 15 year) mass loss history. Such an analysis also provides a baseline for following future changes in Eta Carinae, essential for understanding the late-stage evolution of a nearby supernova progenitor. Our modeling methods can also be adapted to a number of other colliding wind binary systems (e.g. WR 140) that will be studied with future observatories (e.g. JWST).

ONe WD+He star systems as the progenitors of intermediate-mass binary pulsars

Wang, Bo

It has been suggested that accretion-induced collapse (AIC) is a non-negligible path for the formation of the observed neutron stars (NSs). An ONe white dwarf (WD) that accretes material from a He star may experience AIC process and eventually produce intermediate-mass binary pulsars (IMBPs), named as the ONe WD+He star scenario. However, previous studies can only account for part of the observed IMBPs with short orbital periods. In this work, we investigate the evolution of about 900 ONe WD+He star binaries to explore the distribution of IMBPs. We found that the ONe WD+He star scenario could form IMBPs including pulsars with 5-340 ms spin periods and 0.75-1.38 Msun WD companions, in which the orbital periods range from 0.04 to 900 d. Compared with the 20 observed IMBPs, this scenario can cover the parameters of 13 sources in the final orbital period-WD mass plane and the Corbet diagram, most of which has short orbital periods. We found that the ONe WD+He star scenario can explain almost all the observed IMBPs with short orbital periods. This work can well match the observed parameters of PSR J1802-2124 (one of the two precisely observed IMBPs), providing a possible evolutional path for its formation. We also speculate that the compact companion of HD 49798 (a hydrogen depleted sdO6 star) may be not a NS based on the present work.

The interaction of core-collapse supernova ejecta with a companion star

Liu, Zhengwei

The progenitors of many core-collapse supernovae (CCSNe) are expected to be in binary systems. After the SN explosion in a binary, the companion star may suffer from mass stripping and be shock heated as a result of the impact of the SN ejecta. If the binary system is disrupted by the SN explosion, the companion star is ejected as a runaway star, and in some cases as a hypervelocity star. By performing a series of three-dimensional (3D) hydrodynamical simulations of the collision of SN ejecta with the companion star, we investigate how CCSN explosions affect their binary companion. For main-sequence (MS) companion stars, we find that at most 10% of their mass is lost and their resulting impact velocities are less than 100 km/s. The amount of removed stellar mass, the resulting impact velocity, and the chemical contamination of the companion that results from the impact of the SN ejecta strongly increases with decreasing binary separation and increasing explosion energy. Their relationship can be approximately fitted by power laws. Also, we find that the impact velocity is sensitive to the momentum profile of the outer SN ejecta and, in fact, may decrease with increasing ejecta mass, depending on the modeling of the ejecta. Because most companion stars to Type Ib/c CCSNe are in their MS phase at the moment of the explosion, combined with the strongly decaying impact effects with increasing binary separation, we argue that the majority of these SNe lead to inefficient mass stripping and shock heating of the companion star following the impact of the ejecta, causing that the long-term post-explosion evolution of the compaion star is in general not dramatic.

Early Emission through Free Neutron Ejection in Binary Neutron Star Merger

Ishii, Ayako

Gravitational waves (GWs) from a binary neutron star merger (NSM) were observed by advanced LIGO and Virgo on August 2017 for the first time. Soon after the detection, electromagnetic follow-up observations were performed, and the electromagnetic counterpart was detected over the wide wavelength range. The first electromagnetic emission was detected at 10.9 h after the merger event. If the earlier emission from the NSM had been detected, it would have provided us with rich information about the NSM. For example, the ejected material from NSM may include free neutrons in the outermost layer. The layer might contribute the early emission through beta decay in a time scale of hours (Metzger et al. 2015). But the emission powered by decays of free neutrons is not fully understood because the existence of the free neutron layer was explored by smoothed particle hydrodynamics simulation with a small number of particles.   We numerically investigate the possibility for the existence of the free neutron layer and the early emission through decays of free neutrons. We systematically study a wide parameter space of the size of the merging neutron stars and the energy involved in the shock waves. As a result, it is found that the mass of remaining free neutron is 10^{-7} to 10^{-6} Msun, which is smaller than the previously expected by more than two orders of magnitudes. This is due to the p(n, ?)d reaction, which was not taken into account in previous studies. We estimate that the total electromagnetic luminosity is about 4×10^{41} erg s^{-1} at ~30 min after the merger and that the emission has a peak in the ultraviolet wavelengths.

Luminous Blue Variables candidates in M31

Sholukhova, Olga

We present the results of spectroscopic and photometric study of Luminous Blue Variable (LBV) candidates in the Andromeda galaxy. Six targets with optical spectra in M31 galaxy from Massey's list have been observed with the 6-m Russian telescope BTA from 2012 to 2015 in the optical range. The infrared spectra and photometric estimates in the IR bands were obtained with the 3.5-m telescope at the Apache Point Observatory. Using these data in combination with other archive photometric data we produce multi-epoch spectral energy distributions (SED) of these stars. Taking into account an inherent property of LBVs that their bolometric luminosity of LBV stars is constant, we use SEDs to determine the stellar temperatures and radii in different LBV states, as well as the extinction. We use these data to classify of the candidates into three subclass: LBVs or LBV-candidates, B[e]-supergiants and supergiants (dormant LBVs).

The super-Eddington X-ray outburst of SMC X-3: Nearby ultra-luminous X-ray sources and the orbital parameter distribution of Be/X-ray binaries

Townsend, Lee

In 2016, SMC X-3 underwent an long-duration X-ray outburst of extreme brightness. It's luminosity peaked at 1.2 x 10^39 erg/s, making it one of the closest known ultra-luminous X-ray sources (ULX). In light of the recent discovery of ULX pulsars, finding similar systems in nearby galaxies is important as it allows a much more detailed study of the multi-wavelength properties of these systems. I will highlight the recent ULX outburst of SMC X-3 and discuss the other known or potential ULX systems in the Magellanic Clouds.The second part of my talk will focus on the binary parameter distribution of Be/X-ray binaries (BeXRB). I will review the current distribution of parameters in the Galaxy and in the Small Magellanic Cloud (SMC), highlighting the similarities and differences in these populations. SMC X-3 is the 8th system in the SMC to have its orbital parameters determined, adding to the growing number of binaries studied outside of the Milky Way.

MAXI observations of long-term X-ray activities in SFXTs and other HMXB systems

Negoro, Hitoshi

Monitor of All-sky X-ray Image (MAXI) on the International Space Station has been observing all the X-ray sky since August 2009. Super-giant Fast X-ray Transients (SFXTs) are one of interestingobjects of which activities often trigger the MAXI Nova-Alert system(Negoro et al. 2016, PASJ, 68, S1). MAXI detected probable X-ray enhancements from IGR J08408-4503, AX J1739.1-3020, AX J1841.0-0536, and IGR J18483-0311 (e.g., Sakamaki & Negoro 2017, in proc of "7 years of MAXI Monitoring X-ray Transients"). It is difficult to study each enhancement in detail with MAXI data because of poor statistics, but more than 8 years observationsallow us to search periodicity of the enhancements and obtain their average profiles in soft (2-10 keV) X-ray band.To obtain reliable MAXI light curves free from nearby sourcesas best as possible we perform the image fitting analysis for eachscan transit (Morii et al. 2016, PASJ, 68, S11).  We present not only these results, but also  long-termactivities in other HMXBs, for instance, Cir X-1 and black hole candidates,and discuss the origin of the long-term activities.

Hyper-Eddington Soft X-ray Nova from a Be Binary System

Kawai, Nobuyuki

MAXI J0158-744 is an extraordinary soft X-ray transient discovered from a Be system located near the Small Magellanic Cloud.  It is characterized by a soft X-ray spectrum with  little flux above 4 keV, a rapid rise (< 6ks), a short duration (< 11 ks), and a huge peak luminosity of 2x1040 erg/s in 0.7-7.0 keV band with a 0.92 keV Ne emission line.  Its later spectrum resembling "super-soft X-ray source" indicates that the transient event was an explosion on a white dwarf that exceeds the Eddington luminosity by two orders of magnitude.  These properties suggest that the explosion involves a small amount of ejecta and is produced on an unusually massive O-Ne white dwarf close to, or possibly over, the Chandrasekhar limit. We propose that the huge luminosity detected with MAXI was due to the fireball phase, a direct manifestation of the ignition of the thermonuclear runaway process in a nova explosion.  This interpretation has been further supported by the radiative transfer calculation using a Monte Carlo code.

Non-stationary accretion diversities onto black holes of different masses in binary systems

Malanchev, Konstantin

Properties of non-stationary accretion onto black holes of different masses in binary systems are discussed. In a close binary containing a supermassive black hole, a novel sub-critical accretion regime in the innermost radiation-dominated zone of the accretion disk is found, different from accretion regime in stellar mass black hole X-ray binaries. In this regime, the opacity is determined by absorption and not by Thomson scattering. We show that it can be possible to overcome the thermal instability of the innermost zone of the disk to obtain power-law time solutions of the non-stationary accretion onto such massive black holes. The found solutions are applied to explain very luminous optical transients recently discovered in the centres of some active galaxies (e.g., PS1-10adi, Kankare et al. 2017), which are hard to explain as tidal-disruption events. We also discuss the possible role of the outflows and remote gas structures surrounding such binary systems in producing the optical and infrared light curves.

On the origin of supergiant fast X-ray transients

Hubrig, Swetlana

A fraction of high-mass X-ray binaries are supergiant fast X-ray transients.These systems have on average low X-ray luminosities, but display short flaresduring which their X-ray luminosity rises by a few orders of magnitude. Theleading model for the physics governing this X-ray behaviour suggests that thewinds of the donor OB supergiants are magnetized. In agreement with this model,the first spectropolarimetric observations of the SFXT IGR J11215-5952 using theESO FORS2 instrument at the VLT indicate the presence of a kG longitudinalmagnetic field. Based on these results, it seems possible that the keydifference between supergiant fast X-ray transients and other high-mass X-raybinaries are the properties of the supergiant's stellar wind and the physics ofthe wind's interaction with the neutron star magnetosphere.

IGR J16318-4848 : optical and near-infrared spectroscopy of the most absorbed B[e] supergiant X-ray binary with VLT/X-Shooter

Fortin, Francis

The supergiant High Mass X-ray Binary IGR J16318-4848 was detected by INTEGRAL back in 2003 and distinguishes itself by its high intrinsic absorption and B[e] phenomenon. It is the perfect candidate to study both binary interaction and the environment of supergiant B[e] stars. We report on VLT/X-Shooter observations from July 2012 in both optical and near-infrared, which provides unprecedented wide-range, well-resolved spectra of IGR J16318-4848 from 0.5 to 2.5µm. Adding VLT/VISIR and Herschel data, the spectral energy distribution fitting allows us to further constrain the contribution of each emission region (central star, irradiated rim, dusty shell). We derive geometrical parameters using the numerous emitting and absorbing elements in each different sites in the binary. Various line shapes are detected, such as P-Cygni profiles and flat-topped lines, which are the signature of outflowing material. Preliminary results confirm the edge-on line of sight and the equatorial configuration of expanding material, along with the detection of a potentially very collimated polar outflow. These are evidences that the extreme environment of IGR J16318-4848 is ideal to get a better grasp of highly obscured High Mass X-ray Binaries.

Studying the presence of magnetic fields in a sample of high-mass X-ray binaries

Hubrig, Swetlana

Previous circular polarization observations obtained with the ESO FORS1instrument at the VLT in 2007-2008 revealed the presence of a weak longitudinalmagnetic field on the surface of the optical component of the X-ray binaryCyg X-1, which contains a black hole and an O9.7Iab supergiant on a 5.6d orbit.In our poster we report on recently acquired FORS2 spectropolarimetricobservations of Cyg X-1 along with measurements of four additional high-massX-ray binaries.

Chaotic capture and ejection of matter by binary systems

Lages, José

Binaries are everywhere: at the heart of many planetary systems (binary stars), at the center of galaxies (SMBH binaries), among small bodies (binary asteroïds), even the Solar System in a rough approximation can be viewed as the Sun+Jupiter couple. Here, we study the capture of a galactic flow of particles by binaries and even n-aries with a symplectic map description. This approach allows modeling the scattering of 1016 particles after following the time evolution of the captured particle on about 109 orbital periods of the binary system. It is shown that the capture cross-section is much larger than the area of the binary being inversely diverging at small particle energy. We show that the dynamics of captured particles is chaotic and is well described by a simple symplectic map. We obtain the particle density distribution inside such systems and determine in the vicinity of the binary the enhancement factor of their density compared to its galactic value as a function of the mass ratio of the bodies and the ratio of the body velocity to the velocity of the galactic particle wind. We find that the enhancement factor can be on the order of tens of thousands.References:J. Lages, D. Shepelyansky, I. Shevchenko, Kepler map, Scholarpedia, 13(2):33238 (2018)G. Rollin, J. Lages, D. L. Shepelyansky, Chaotic enhancement of dark matter density in binary systems, A&A 576, A40 (2015)J. Lages, D. L. Shepelyansky, Dark matter chaos in the Solar System, Monthly Notices of the Royal Astronomical Society : Letters 430, L25-L29 (2013)

Firm Detection of 7-Year X-ray Periodicity from X Persei

Nakajima, Motoki

X-ray binary pulsars exhibits various time scale activities.These variabilities are considered to be produced by the rotation of the neutron star, the binary orbital motion, and the precession of the accretion disc around the neutron star (so called superorbital).Each time scale distributes in the time range from few milliseconds to months.In addition to the above periodicities, Laplace et al.\ (2017) reported that Be/X-ray binary pulsar EXO 2030+375 repeats the giant X-ray outburst and the outburst phase shift with the time interval of ~10 years.In order to explain such long-term recurrence period, Kozai-Lidov oscillation model was proposed, and the estimated period was similar to the observed time interval of ~10 years.Except for EXO 2030+375, there are no reports about the sources which shows a periodicity more than several years, so far.To search for another source having long periodicity, we analyzed one of the Be/X-ray binary pulsar, X Persei, observed by RXTE/ASM, Swift/BAT, and MAXI/GSC.This source is characterized by a spin period of ~835 s, an orbital period of 250.3 days, an ecccentricity of 0.11 (Delgado-Marti et al.\ 2001).No normal outburst have been recorded from this source, however, it was observed that its X-ray flux has increased about twice every 7-years since 2003.Furthermore, it was confirmed that the decrease timescales (~250 days) are the same for all three X-ray flares.

X-Ray Binaries as Gravitational Wave Sources

Yakut, Kadri

We catalogued well-determined physical parameters of low-mass X-ray binary (LMXB) and high mass X-ray binary (HMXB) systems. Angular momentum loss (AML) mechanism via gravitational radiation (GR) and magnetized stellar winds (MSW) are calculated for some LMXB and HMXB systems. Gravitational wave amplitudes (h) of the relatively short period X-ray binary systems have been compared with the limit of the Laser Interferometer Space Antenna (LISA).

Orbital resolved spectroscopy of GX 301-2: wind diagnostics

Islam, Nazma

GX 301-2, a bright high-mass X-ray binary with an orbital period of 41.5 days, exhibits stable periodic orbital intensity modulations with a strong pre-periastron X-ray flare. Several models have been proposed to explain the accretion at different orbital phases, invoking accretion via stellar wind, equatorial disc, and accretion stream from the companion star. From the orbital resolved spectroscopic study of GX 301–2 with the X-ray all sky monitor MAXI, we found a very large equivalent width of the iron line for a small value of the column density in the orbital phase range 0.10–0.30 after the periastron passage. The orbital dependence of the spectral parameters favours accretion on to the neutron star occurring via a high density accretion stream plus stellar wind of the companion. We further investigate the characteristics of the accretion stream with an ASTROSAT LAXPC and SXT observation of the system. 

A curious case of HMXB 4U 1700-37

Islam, Nazma

4U 1700-37 is an eclipsing High Mass X-ray binary in a short orbital period of 3.412 days. In the absence of detectable pulsations, the orbital evolution is determined from the eclipse timing measurements, both from archival measurements as well as new measurements from long-term light curves obtained with the all sky monitors RXTE-ASM, Swift-BAT and MAXI-GSC. The orbital period decay rate of the system is estimated to be 10^{-7} /yr, smaller compared to its previous estimates. The mid-eclipse times and the eclipse duration measurements obtained from 10 years long X-ray light curve with Swift-BAT are used to separately put constraints on the eccentricity of the binary system and measure any apsidal motion. We carry out a deepest search for pulsations and Cyclotron Resonance Scattering Feature (CRSF) using a 40 kilosec ASTROSAT LAXPC observation. These results will provide some newer insights into the nature of the compact object, which is either a very high mass neutron star or a very low mass black hole.

Ultra-luminous X-ray sources as neutron stars propelling and accreting at super-critical rates in high-mass X-ray binaries

Erkut, M. Hakan

Ultra-luminous X-ray sources (ULXs) are thought to be a heterogeneous group consisting of either the intermediate mass black holes accreting matter at critical (Eddington) rates or stellar mass black holes or neutron stars accreting matter at super-critical rates. There is growing evidence following the discovery of pulsating ULXs that accreting neutron stars in high-mass X-ray binaries (HMXBs) form a subclass and might even be common within the present population of ULXs. The earliest stage of HMXBs may harbor rapidly rotating neutron stars propelling out the matter transferred by the massive companion. The newly born ULXs may therefore emerge as super-critical propellers manifesting super-Eddington luminosities through the spin-down power transferred by the neutron-star magnetosphere to the accretion disk. In this picture, pulsating ULXs appear as super-critical mass-accreting descendants of non-pulsating young ULXs. We present this evolutionary scenario within a self-consistent model of magnetosphere-disk interaction and discuss the implications of our results on the spin and magnetic field of the neutron star.

Pecularities of super-Eddington flares from HMXB LMC X-4 with NuSTAR

Shtykovsky, Andrey

We present the results of analysis of high-mass X-ray binary LMC X-4 using the NuSTAR observatory data. We discuss pecularities appearing during pulsar switching into ultraluminous state (peak luminosity Lx ~ (2 - 4) × 1039 erg/s). The pulsar spectrum is well approximated by the thermal Comptonization model (comptt) both in a quiescent state and during flares. The order of magnitude increase in luminosity during flares is observed primarily at energies below 25–30 keV, whereas at higher energies (30–70 keV) the shape of the spectrum and the source flux remain practically unchanged. The pulse profile during ultraluminous increase of the pulsar luminosity in the energy range of 3–40 keV becomes approximately triangular, and the pulsed fraction increases with increasing energy, reaching 60–70 % in the energy range of 25–40 keV. We discuss possible changes in the geometry and properties of the accretion column, which can explain variations in spectra and pulse profiles.

The 17 pairs of double neutron star systems and their evolutionary links with HMXBs

Zhang, Chengmin

For the observed 17 pairs of double neutron star systems, we analyze their eccentricity and orbital period, and find that theses DNSs can be classiffied into theee types, which may correspond to the NS formation history, e.g. by supernova or electron capture. Their relations with the progenitor HMXBs are investigated. We simulate the processes, with various initial conditions, and the observed DNS distribution can be satisfactorily explained.

Studying the circumstellar environments of B[e] supergiant binaries using high-cadence optical spectroscopy

Porter, Augustus

B[e] supergiants, supermassive stars exhibiting the B[e] phenomenon of strong Balmer line emission and forbidden line emission, are a rare and thereby poorly understood class of star. Both their formation pathways and the origin of their B[e] phenomena remain unclear. I will present a case study of GG Carinae (GG Car), a little studied and eccentric Galactic B[e] supergiant binary, based on successive Global Jet Watch spectroscopy data which has been collecting high-time-sampled optical spectra since early 2015. I use Fourier analysis to examine the behaviour of the orbital period of the inner binary, and how this is manifested in the circumstellar environment. I will also present an analysis of forbidden emission lines that have very different temporal characteristics from those that depend straightforwardly on the orbital period, and their connection to the circumbinary-orbiting material in this system. The equivalent width of the Ha line in GG Car is strongly dependent on the period of the inner binary, suggesting that the amount of emitting circumstellar matter varies strongly with orbital phase due to alternating accretion/decretion of material from the stellar surfaces. Despite GG Car having so far not been observed in the X-Ray band, if the secondary is a compact object then the system is similar in phenomenology to variable X-Ray binary sources consisting of classic Be and neutron stars, and the study of GG Car can shed further light on the physics of X-Ray binaries.

Probing the building blocks of galaxies: sub-galactic scaling relations between X-ray luminosity, SFR and stellar mass.

Kouroumpatzakis, Konstantinos

We explore the tight correlation between the X-ray luminosity from high mass X-ray binaries (HMXBs), star formation rate (SFR), and stellar mass using the Star-Formation Reference Survey (SFRS), a sample of galaxies representative of the star-formation activity in the local Universe. We measure these relations with archive X-ray Chandra and XMM observations and a comprehensive set of star-formation (radio, FIR, 24µm, 8µm, Ha, UV, SED fitting) and stellar mass (K-band, 3.6 µm, SED fitting) indicators. We investigate the X-ray luminosity – SFR – stellar mass scaling relations down to sub-galactic scales of ~1 kpc2, extremely low SFRs (~10-6 Msol/yr) and stellar masses (~104 Msol). Using different age-sensitive SFR indicators, we quantify the scatter and dependence on the age of the local stellar populations. These results importantly set the benchmark for the formation of X-ray binaries in vigorous, but low SFR galaxies in the early Universe.

First Constraints on Empirical Mass-Loss Rates from Magnetic O-stars using Ha Emission

Driessen, Florian

Over the past decade, large survey programs have revealed that roughly 10 % of all massive main-sequence stars harbor large-scale, strong, and organized surface magnetic fields. However, such massive stars also experience powerful starlight-driven wind outflows. Due to the presence of magnetic fields these stellar outflows are consequently magnetically confined. In the case of slowly rotating O-stars being studied in this work, stellar wind material along closed field loops falls back onto the stellar surface due to a cooled downflow. Yet, the transient suspension of material within the loops leads to statistically overdense regions centered at the magnetic equator. The emerging structure, known as a Dynamical Magnetosphere (DM), results in rotational phase modulations of key diagnostic wind lines such as Ha.Using full 3D radiative transfer together with an analytic description of DMs, this poster will present the first results regarding the derivation of empirical mass-loss rates from magnetic O-stars. We infer the mass loss rate by fitting the synthetic Ha emission to observations, a procedure quite analogous to what is being done when deriving mass-loss rates for non-magnetic O-stars, except for the rotational modulation. Obtaining such empirical constraints are of critical importance since the mass-loss “quenching” of the magnetic field is also predicted to have significant effects on the further evolution of the star, e.g., magnetic braking. Moreover, recent results have even suggested Galactic magnetic massive stars to be possible progenitors of “heavy” stellar-mass black holes such as those that led to the ground-braking detection of gravitational waves by the LIGO-Virgo consortium.

Clarifying the population of HMXBs in the Small Magellanic Cloud

Maravelias, Grigoris

The Small Magellanic Cloud (SMC) hosts a large number of High-mass X-ray binaries (~120) offering a unique laboratory to examine these sources with a homogenous and consistent approach. Almost all the sources with confirmed counterparts have as a companion an OB star with an equatorial decretion disk. This makes their population to stand out in ?a imaging and, subsequently they display strong emission Balmer lines. However, for a large fraction of the HMXB population in the SMC, although they are associated with one or more early-type stars, the actual counterpart and its nature are unclear. Thus, we performed extensive photometric and spectroscopic surveys to identify the optical counterparts to HMXB candidate sources. Using ?a imaging we discover that the OBe stars, i.e. the parent population of HMXBs, is ~13% of the total OB star population in the SMC down to 18.7 mag (equivalent to ~B8 type Main Sequence stars). Using this catalog we perform a cross-correlation with the most recent census of X-ray sources in the SMC (Haberl and Sturm, 2016) to verify the nature of known HMXBs and explore a number of candidate systems, in combination with spectroscopic observations. Moreover, using the most recent census of star clusters in the SMC (Bitsakis et al., 2018) we investigate the connection of the HMXBs with star-clusters and we use it to obtain a robust estimate of their kick velocities.

Accretion and ejection coupling during the giant flares of Cygnus X-3

Egron, Elise

Cygnus X-3 is a high-mass X-ray binary (HMXB) that consists of a compact object wind-fed by a Wolf-Rayet star. The nature of the compact object is still uncertain, but a black hole seems to be favored. Cyg X-3 is the brightest microquasar at radio frequencies, showing giant radio flare episodes with uncommon flux densities up to 20 Jy. These spectacular and rare events give unprecedented opportunities to better understand the relationship between accretion state and jet launching mechanisms, and to compare the effect of accretion geometry (companion star, orbital parameters) to other HMXBs. After more than five years of quiescent state (0.1-0.2 Jy), Cyg X-3 underwent two giant flares in September 2016 and April 2017. These events occurred a few weeks after the source performed a transition to the quenched radio state (< 0.03 Jy). A transition from the ultra-soft X-ray state to a harder X-ray state was clearly visible at the onset of the giant radio flares, together with a gamma-ray emission registered with AGILE and Fermi/LAT. The radio emission of the two last giant flares was monitored with SRT (64-m) and Medicina (32-m) in order to follow the evolution of the flare on a hourly scale. Rapid flux variations were observed at high radio frequencies (18-25 GHz) at the peak of both flares, together with a rapid evolution of the spectral index (from 0.4 to 0.6 with S ? ?^(-a) in less than 5 hours. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin ejecta in expansion moving outwards from the core.

Implications of a density dependent IMF for the statistics of progenitors of gravitational wave sources

Kavila, Indulekha

Observations of multi-compact-object mergers taking place in galaxies offers a window to massive star formation in globular clusters, the oldest objects in the Universe.  The advent of next generation telescopes like the James Webb Space Telescope and the TMT allow detailed exploration of binaries, and their statistics in deeply embedded star burst as well as globular cluster fields.  The advent of Advanced LIGO and LISA leads us to multi-messenger astronomy that includes multi-wavelength observations on multi-compact-object mergers in the GW sector too.  More and more sophisticated codes allow us to track the formation and evolution of binaries in stellar clusters and details of the evolution and merger of multi-compact-object systems, from the very early phases of high stellar density and high density of embedding gas to late phases wherein massive compact objects merge.  In simulations of binary formation and evolution in globular clusters, the possibility that the distribution in the properties of the initial set of binaries might have a non-standard IMF factored into them, has not been explored.  Observations of the nearest high mass star forming regions point to the IMF at the high mass end being flatter than Salpeter in regions where the stellar densities are high.  We explore the impact of the distribution in the properties of the initial set of binaries that have a non-standard IMF factored into them, on the statistics of potential gravitational wave sources in the Galaxy derived from simulations. Globular clusters being significant contributors to the ionization history of the early universe, the results have implications for the same, and also on our ability to explore the putative mass gap between the upper limit for neutron star masses and the lower limit for black hole masses.  Priors with different assumptions regarding the IMF from which the binaries are drawn, changes the derived most likely masses as well as the confidence intervals on them.

Mildly Super-Eddington mode of X-ray pulsars

Arefiev, Vadim

We consider observational appearances of several X-ray pulsars and discuss possible application to the modern models of  X-ray emission generation in accreting pulsars with strong magnetic field.  In particular we consider the arising limitations on properties of accretion column, based on found results.

Vertical distribution of HMXBs in NGC 55: Constraining their centre of mass velocity

politakis, babis

SN induced kicks are a key parameter in the formation and evolution of X-ray binaries and their descendants such as short Gamma Rey Bursts and gravitational wave sources. Edge-on galaxies provide a unique environment for directly measuring the offset of X-ray binaries from their birth places due to SN kicks. We present a study of the spatial distribution of HMXBs in NGC55 our nearest edge-on galaxy. We find that the vertical distribution of HMXBs is puffed-up compared to the distribution of star formation. We model this effect with a smearing gaussian with a s ~ 0.43 kpc. Given the average travel time of HMXBs we find a center of mass velocity of 36 km/s, consistent with similar estimations in the Milky Way but higher than the Magellanic Clouds, in agreement with models for higher fraction of electron capture SN in lower metallicity environments.  

Optical variations of selected LMXB and HMXB systems with neutron star

Icli, Tugce

Long-term and short-term photometric variation of the selected LMXBs and HMXBs with neutron star component are studied. We obtained new VRI observations of the selected systems by using 60cm Robotic telescope and 100cm telescope at the TÜBITAK National Observatory (TUG). We combined all the available observations of the systems with our new observations. Long- and short period light variation are discussed in this study.This study is supported by the Turkish Scientific and Research Council-TÜBITAK (117F118). We thank to TUBITAK for a partial support in using T100 and T60 telescope with project number 15AT60-776, 15CT100-916 and 17BT100-1204.

Modeling of hydrodynamic processes within high-mass X-ray binaries

Kurfürst, Petr

High-mass X-ray binaries belong to the brightest objects in the X-ray sky. The massive X-ray binariesmay be schematically sub-divided into supergiant X-ray binaries and Be/X-ray binaries. The firstsubclass usually consists of massive O or B star, or a blue supergiant while the compact, X-rayemitting, component is a neutron star or black hole. The Be/X-ray binaries consist of a Be star andmostly a neutron star. Intensive matter accretion from luminous optical donor star onto the compactobject takes various forms: spherically symmetric accretion, Roche-lobe overflow, or circumstellardisk. It produces an intensive X-ray source that may more or less dramatically vary in brightness ontimescales ranging from miliseconds to years. In our multi-dimensional models we perform numericalsimulations of an accretion of a circumstellar disk matter onto a compact companion in case of Be/X-ray binaries. Using the Bondi-Hoyle-Littleton approximation, we estimate the neutron star accretionrate and the X-ray luminosity of a system, we can determine the Be/X-ray binary disk hydrodynamicstructure and compare its deviation from the isolated Be stars’ disk. From the rate and morphologyof the accretion flow and the X-ray luminosity we improve the estimate of the disk mass-loss rate.We also study the behavior of high-mass X-ray binary system under a supernova explosion event,assuming a blue supergiant progenitor with an aspherical circumstellar environment.

The spectroscopic evolution of PSR J2032+4127 gamma-ray binary during its periastron passage.

Echevarria, Juan

We present the results of our optical monitoring of PSR J2032+4127 gamma-ray binary around its periastron passage on November 13th, 2017. The compact object in the binary is a highly magnetized neutron star (B~1012 G) that follows an extremely eccentric orbit around the Be star MT91{213} companion. The PSR J2032+4127 is a long orbital-period (49 years) transient lying at a close distance of 1.33 kpc, which makes it an ideal observational target.We observed PSR J2032+4127 with the 2.1m telescope from San Pedro Mártir observatory (México) using the Boller & Chivens spectograph. Our monthly monitoring campaign covered the timeframe from September to December so that we could follow the evolution of the system before, during and after the periastron. In this poster we will present our preliminary results of the observations, focusing on the evolution of the H-alpha profile as well as paying special attention to any characteristic features that may evolve during the passage.The study of this binary close to its periastron passage broadens our knowledge about how interaction works in gamma-ray binaries, and gives us new insights on the accretion physics at play in these kinds of systems. 

Optical Monitoring of High Mass X-ray Binary Systems with Black Hole Component

Kocak, Dolunay

We presented long term optical observations of the selected high mass X-ray binaries with black hole components. New observations obtained by using the 1m and 0.6m telescopes at the TÜBITAK National Observatory (TUG). Photometric behaviors of the systems are analyzed and compared with the earlier published results. We will discuss new observations results in this study.This study is supported by the Turkish Scientific and Research Council-TÜBITAK (117F118). We thank to TUBITAK for a partial support in using T100 and T60 telescope with project number 15AT60-775, 15CT100-916 and 17BT100-1204.

Spectroscopic identification of INTEGRAL high-energy sources using VLT/ISAAC

Fortin, Francis

INTEGRAL has been observing the gamma-ray sky for 15 years and discovered over 900 high-energy sources of various nature (Bird et. al 2016). They are mostly AGNs (369) and X-ray binaries (348). However, more than 200 of them still lack a precise identification. We thus aim to better constrain their nature in order to improve the census on binaries, which could then be compared with population synthesis models. We performed near-infrared photometry and spectroscopy with VLT/ISAAC in July 2012 on 15 INTEGRAL sources, and identified them by comparing their spectral features to nIR atlases. In particular, deriving the spectral type of donor stars allowed us to constrain the exact nature of several binaries. Our sample is mostly composed of AGNs (5) and Cataclysmic Variables (5), along with X-ray binaries (2 BeHMXB and 2 LMXB). Especially, some of the CVs we found appear to have a companion star which may have depleted its atmosphere. These results are the first step to further studies which will focus on deriving various parameters in binaries using spectral modelisation.

The Very Young Be-Star X-ray Binary Circinus X-1

Schulz, Norbert

Accretion conditions and morphologies of X-ray transients containing neutron starsare still poorly understood. Circinus X-1 is a specifically enigmatic case where we observe X-ray flux changes covering four orders of magnitude. We observed Circinus X-1 many times since the launch of the Chandra X-ray Observatoryusing the high energy transmission grating spectrometer andeach time the source gave us a vastly different look. Most recently we caught the source at its very lowest X-ray flux at a flux of 1.8×10-11 erg cm-2 s-1.Its spectrum, a single 1.7 keV blackbody spectrum, showed a low emission radius of 0.4 kmwhich implies a high magnetic field between 1.7 and 4.8×1011 G depending on neutron star radius. Photoionized line emissions suggesta large emission volume and low plasma densities. The observed bluehifts of ~400 km s-1and emission volume is consistent with the ionized but distorted wind of a B5Ia supergaint companion confirming a previous identification. We argue that the companion of Cir X-1 isfast rotating Be-star and its stellar disk provides much of the                   observed excess column densities. We paint a scenario in which a precessing oblateBe-star rotator may explain the vast X-ray flux variations in the past.

Viscous-warp instability in accretion discs

Dogan, Suzan

Accretion discs are the essential ingredient for a wide range of astrophysical phenomena, including star and planet formation, X-ray binaries and active galactic nuclei. Through several different effects, discs can warp. If a warp in a disc is too large, the disc can break apart into two or more distinct planes. Further if an initially planar disc is subject to a strong differential precession, then it can be torn apart into discrete annuli that precess effectively independently. Disc tearing has been shown to occur in discs inclined to the spin of a central black hole, in circumbinary discs around misaligned central binary and in circumprimary discs misaligned with respect to the binary orbital plane. As disc tearing promotes markedly enhanced and variable accretion, it has significant implications for a variety of astrophysical systems: e.g. outbursts in X-ray binaries and fuelling SMBH binaries. The criterion for disc tearing has previously been derived simplistically by comparing the viscous torque with the precession torque. In this work, focusing on the diffusive regime, we investigate the stability of warped discs to determine the precise criterion for an isolated disc to break. The instability appears in the form of viscous anti-diffusion of the warp amplitude which leads to a discontinuity in the disc angular momentum. The physics of ‘the viscous-warp instability’ can be understood as a combination of two terms: 1) a term which would generally encapsulate the classical Lightman-Eardley instability in planar discs but is here modified by the warp to include  and 2) a similar condition acting on the diffusion of the warp amplitude. This instability underlies the process of disc tearing which has capacity to dramatically alter the instantaneous accretion rate and observable properties of the disc on short timescales. I will present a comprehensive analysis of ‘the viscous-warp instability’ and the emergent growth rates and their dependence on disc parameters.

X-ray spectroscopy of massive stellar winds: previous and ongoing observations of the hot star zeta Pup

Nichols, Joy

The massive stellar winds of hot stars have an important impact on galactic evolution, yet their structure and internal processes remain only partially understood. One of the best nearby laboratories for studying such massive stellar winds is the O4 If star zeta Pup. After reviewing existing X-ray observations from Chandra and XMM, we present a simulation of an 840 ksec upcoming Chandra HETGS observation. This simulation indicates that the increased S/N of this new observation will allow several major steps forward in the understanding of massive stellar winds. By measuring X-ray line strengths and profiles, we should be able to differentiate between various stellar wind models and map the entire wind structure in temperature and density. This legacy X-ray spectrum of zeta Pup will be a useful benchmark for future X-ray missions.

Studying the accretion geometry of X-ray pulsar GX 1+4 in a peculiar state

Jaisawal, Gaurava K

We present detailed spectral and timing studies using a NuSTAR observation in 2015 October of GX 1+4 during an intermediate intensity state. The measured spin period of 176.778 s is found to be one of the highest value since its discovery. In contrast to a broad sinusoidal-like pulse profile, a peculiar sharp peak was observed in profiles below 25 keV. The profiles at higher energies were found to be significantly phase-shifted to the soft X-ray profiles. Broadband energy spectra of GX 1+4, obtained from NuSTAR and Swift observations, were described with various continuum models. Among these, a two component model consisting of a bremsstrahlung and a blackbody component was found to best-fit the phase-averaged and phase-resolved spectra of the pulsar. Physical models were also used to investigate the emission mechanism in the pulsar. Based on the results obtained from fitting physical models to the data, the magnetic field strength of GX 1+4 was estimated to be in ~(5--10)x10^12 G range. Phase-resolved spectroscopy of NuSTAR observation showed a strong blackbody emission component in a narrow pulse phase range. This component was interpreted as the origin of the peculiar peak in the pulse profiles below 25 keV. The size of emitting region was calculated to be ~400 m. The bremsstrahlung component was found to dominate in hard X-rays and explains the nature of simple profiles at high energies.

Ultraluminous X-ray sources as the brightest HMXBs

Roberts, Tim

The link between ultraluminous X-ray sources (ULXs) and high mass X-ray binaries (HMXBs) is now well-established, with the majority of observed ULXs thought to constitute a compact object (black hole or neutron star) feeding from a young and massive star.  We present a new catalogue of 403 ULXs and 1064 less luminous point X-ray sources associated with nearby galaxies, derived from the 3XMM-DR4 catalogue, the majority of which we expect to be HMXBs.  The applications of this catalogue are numerous: for example the identification of high amplitude long-term variability in ULXs, a possible indicator of pulsar ULXs transiting in and out of the propeller state; identifying new IMBH candidates from the most luminous ULXs; and extending detailed spectral-temporal studies from bright ULXs down to objects in the Eddington threshold regime (~1039 erg s-1).  We can also begin to systematically examine the properties of HMXBs in nearby star-forming galaxies that possess sub-ULX luminosities, where large datasets exist.  We present early results from stacking analyses that seek to do this, and argue why understanding these objects is important for understanding galaxy evolution at high redshifts.

The X-ray Binary Populations of M81 and M82

Sell, Paul

We present a detailed study of the X-ray point source populations of the nearby, star-forming, spiral galaxy M81.  Using deep HST data, we uniquely classify the X-ray binary (XRB) populations on the basis of their donor stars and local stellar populations.  We measure the X-ray luminosity functions (XLFs) of the different XRB sub-populations (early-type main sequence, supergiant, low-mass, globular cluster), and we compare these results with predictions from XRB population synthesis models.  This more robust classification (than the common, simple bulge/disk spatial separations) of XRBs minimizes contamination between different sub-populations, and it shows that high-mass XRBs have steeper XLFs than the “canonical” star-forming galaxy XLF commonly used.  In the case of globular clusters, we find that more massive and denser globular clusters are more likely to be associated with XRBs.  We also compare these results with the XRB populations of the prototypical starburst galaxy, M82, for which we present the deepest XLF reported for a starburst galaxy.  We discuss the variations of the XRB populations in regions of M82 dominated by star-formation episodes at different ages, and in the context of predictions from XRB formation and evolution models.

Sub-galactic regions on the galaxy-wide scaling relations: the example of the ULX-rich galaxies NGC 3310 and NGC 2276

Anastasopoulou, Konstantina

We present results from Chandra observations of the X-ray starburst galaxies NGC 3310 and NGC 2276. We detect 30 discrete sources with luminosities above 2.0x1038 erg/s in NGC 3310, and 19 discrete sources with luminosities above 1.0x1038 erg/s in NGC 2276. The majority of the sources have photon indices of 1.7-2.0, typical for X-ray binaries. Both galaxies have large numbers of ultra-luminous X-ray sources (ULXs): 14 for NGC 3310 concentrated on the circumnuclear star-forming ring and north spiral arm, and 11 for NGC 2276 with the brighter ones on the west side of the galaxy which is compressed due to harassment by the intra-group medium it is moving into. We find for both galaxies that the ULX-hosting areas show excess X-ray luminosity with respect to the general scaling relations between X-ray binary luminosity, SFR, and stellar mass. On the other hand, other regions of the galaxies either agree or fall below these scaling relations. This indicates that sub-galactic regions do not necessarily follow the galaxy-wide scaling relations. The significant deviation from the average galaxy-wide scaling relation can be attributed to either age or metallicity variations between sub-galactic regions, with the former being more likely. Such differences in age could be the origin of the scatter we observe in the low SFR regime of the LX-SFR scaling relations. 

Constraining the blackhole masses from elemental abundances of nearby stars

Kobayashi, Chiaki

First of all, I will show the contribution of massive stars in galactic chemical evolution, namely, the improtance of hypernovae from >25Msuns stars. Secondly, provided that the interstellar medium was highly inhomogeneous at the early stage of galaxy formation, we constrain the properties of the first supernovae (from <50Msun stars) by directly comparing our nucleosynthesis yields to the observed elemental abundance patterns of extremely metal-poor stars in the solar neighborhood. We have done this abundance fitting analysis for ~200 stars, and the predicted mass distribution has a double peak at ~6 and ~10 Msun. Finally, I will discuss the contribution from stars with >50Msun by searching very low [alpha/Fe] stars in the Milky Way.

Understanding Accretion Effects in Disks in HMXBs

Montgomery, Michele

During the HMXB phase, the companion to the more massive black hole or neutron star primary evolves, losing its mass to the primary. The lost mass is thought to form an accretion disk around the primary, which can then heat up due to friction within the disk. This heating, along with the jets that form from the primary generate the X-ray emission. Accretion disks are also suggested to occur in BeHNXBs due to the type II outbursts and QPOs that are observed. The flare-like activity during the outburst is large-scale and may be caused by instabilities near the inner edge of the accretion disk that could oscillate the accretion flow. In this work, we study effects of accretion stream on an accretion disk. We know from studies of their low-mass close binary counterparts, that gas stream overflow can impact the disk face, generating local X-ray emission. In this work, we study the net effect on the disk due to the local heating of gas stream overflow. We present our findings of effects within the disk due to gas stream overflowing the edge of an accretion disk that surrounds a high mass compact primary in a close binary.

Intermediate luminosity optical transients: the case of Eta Carinae

Grant, David

Between the well studied classes of supernova explosions and nova eruptions, a large luminosity gap exists. Intermediate luminosity optical transients (ILOTs) are a diverse group of stellar systems, known to exhibit peak luminosities within this range and are becoming an evermore exciting class of laboratories for studying outflows and binary stellar evolution. I will present a detailed analysis of the massive stellar binary Eta Carinae, comprising a massive main-sequence star and a luminous blue variable that has erupted dramatically in its past: this system is often regarded as a supernova imposter. My investigations are based on optical spectroscopy from the Global Jet Watch observatories, giving highly time-resolved dynamical information, over a 4-year period, spanning periastron. This unique dataset allows us to elucidate the evolving dynamics of the system giving us insights into one of the most famous ILOTs known today.

Binary Population Synthesis with Markov-chain Monte Carlo

Andrews, Jeff

Nowhere is our understanding of binary evolution challenged more than in the formation of the merging double neutron stars (DNS) recently detected by gravitational wave observatories. Yet, exactly because these systems are so sensitive to binary evolution physics, they have the most potential to constrain theory. These constraints are traditionally placed using binary population synthesis, a method that, despite its potential, has difficulty generating sufficient statistics because merging DNSs are exceedingly rare; only a small fraction of simulated systems evolve into binaries similar to those observed. I will introduce a fundamentally new approach to studying stellar binary populations that employs a Markov-chain Monte Carlo algorithm to efficiently explore the binary evolution parameter space. In addition to being substantially more efficient than traditional methods for studying high mass binaries, this technique seamlessly incorporates observational constraints and their corresponding uncertainties. As a test case, I apply this method to model the population of high mass X-ray binaries in the Large Magellanic Clouds. Finally, using this approach I will demonstrate what we can learn about the formation and evolution of the merging compact objects detected by LIGO.

X-raying the clumpy stellar wind in the high-mass X-ray binary Cyg X-1

Hell, Natalie

Supermassive O/B-type stars exhibit strong stellar winds. Due to instabilities the hot wind material is prone to fragment into clumps of colder and denser material. The detailed structure of the wind and the clump morphology are still not well understood. In high-mass X-ray binaries (HMXBs), where these stars are paired with a compact object, the interaction with the compact object alters the wind structure further.Cyg X-1 is a persistent black hole HMXB with a supergiant O9.7Iab type star whose strong stellar wind is focused onto the black hole. The black hole is powered by accretion of the clumpy wind and the resulting continuum radiation is a perfect backlighter to X-ray and study the properties of the focused stellar wind. As the clumps pass our line of sight to the black hole, they cause excess absorption visible as dips in the observed X-ray lightcurves. The absorbing material imprints characteristic spectral signatures onto the continuum radiation from the black hole, depending on density, temperature, ion content (including a wide range of charge states), and velocity of the material. High-resolution spectroscopy enables us to use plasma diagnostics of Doppler shifts and line ratios of these signatures to determine the properties of the absorbing material. Analysing and comparing these high-resolution spectra at periods of different absorption levels, corresponding to different phases of the wind, thus allow us to put constraints on the size, morphology and distribution of the clumps. Here, we present our results of the clump characterstics derived from gratings observations of Cyg X-1 and discuss them in comparison to findings from other methods and to predictions of wind models.Work by LLNL was performed under the auspices of the U.S. DOE under Contract No. DE-AC52-07NA27344.

Detection of the Progenitors of Be X-ray Binaries

Gies, Douglas

Be stars are rapidly rotating, non-supergiant B-type stars that ejectequatorial disks.  Many of these stars may have been spun up throughmass transfer in a close binary system, in which case the formermass donor star is now a hot, stripped-down, subdwarf.  There are a few known cases of Be stars with hot subdwarf (sdO) companionsthat were discovered through International Ultraviolet Explorer (IUE) spectroscopy.Here we report on the search for Be+sdO candidates using archival FUV spectra from IUE.Our search strategy involves calculation of a cross-correlation funtion (CCF)of each observed spectrum with a model spectrum for T_eff = 45 kK,the typical value for the known subdwarf companions.   We collected IUEspectra for 264 targets, and selected for closer examination thosewith a CCF peak greater than three times the background CCF noise.We applied two selection criteria to select candidate Be+sdO binaries:targets showing a significant and narrow CCF feature (with a half-width muchsmaller than the projected rotational velocity of the Be star) andalso displayed radial velocity shifts indicative of orbital motion.  We identified eight candidate systems that met both criteria plusfour other candidate systems with strong peaks but too few spectrato confirm orbital motion.  These are important targets for follow upspectroscopy.  The new plus known Be+sdO binaries comprise about 6% of the sample.This fraction is consistent with the idea that we only find sdO companionsin their relatively short and bright evolutionary stage of He-shell burning,while the majority of He-core burning companions are too faint to detectwith current methods.  The subdwarf component in some of these systemsis destined to explode as a H-deficient supernova and leave a neutron starremnant.  This is the stage of the Be X-ray binaries, the most commonkind of massive X-ray binary.

Classical Be stars as Mass Donors in Be/X-ray Binaries

McSwain, M. Virginia

Roughly half of known high mass X-ray binaries contain a Be star secondary.  These Be/X-ray binaries (BeXRB) are known to experience a diverse assortment of X-ray outbursts, some of which (Type I) may be associated with a binary periodicity while others (Type II) are seemingly more random.  At least some Type II outbursts may be related to the changing disk state of the mass donor, a classical Be star.  Here we present properties of the optical variability of classical Be stars to compare their optical outbursts with their X-ray counterparts to look for links behind the two phenomena.  While the duration of optical outbursts is consistent with the "zoo" of BeXRB outbursts presented in the preliminary catalog of Kuhnel et al., the shapes of optical outbursts reveal more diversity.

Binary nature of fast rotating Be star Pleione and the reflection to it's circumstellar disk evolution

Iliev, Lubomir

Pleione is a classical Be star well known with it’s cyclic transitions between Be-, shell- and normal B spectral phases.It’s nature as a binary system was discussed by McAlister et al. (1989), Gies et al. (1990), Luthardt & Menchenkova (1994) and Nemravova et al. (2010). We present results of the tracing the evolution of the dimensions of emitting regions of the circumstellar disk of Pleione connected with the binary nature of the star.

An X-ray study of Wolf-Rayet binaries

Sugawara, Yasuharu

We present the results from the X-ray spectral analysis of the WR+O colliding wind binaries. Wolf-Rayet binaries represent an important stage in the evolution of massive binary systems. In addition, some colliding wind binaries show periodic infrared excess, indicating periodic dust formation. These winds affect the circumstellar environment. The X-ray spectrum is the best measure of conditions in the hot postshock gas, and the crucial time for observations is around periastron passage when densities and emitting volume are changing most rapidly. We performed the X-ray spectral analysis of the WR+O colliding wind binaries. As the results, these X-ray spectra show the phase-locked variations. In this paper, we will report the wind properties of these binaries, and discuss the effect for the circumstellar environment.

On the formation of black holes in High-mass X-ray Binaries

Batta, Aldo

High-mass X-ray binaries (HMXRBs), such as Cygnus X-1, host some of the most rapidly spinning black holes (BHs) known to date. However, spin measurements from LIGO events produced by the mergers of binary black hole systems with masses ranging from 7 to 36 solar masses have low effective spins, consistent with low spin values. Assuming that the BH spin comes from the direct collapse of the star, we study the evolution of BH properties (mass and spin) as it accretes shells of infalling material from 1D stellar profiles with different rotation. When feedback from the formation of an accretion disk around the BH is included, the integrated feedback is large enough to unbind the collapsing star. If this energy is efficiently deposited into the infalling layers the collapse of the star will be halted, yielding BHs less massive and with a smaller spin that the one expected from the entire collapse of the star.

Constraints on Estimation of Radius of Double Pulsar PSR J0737-3039A and Its Neutron Star Nuclear Matter Composition

Chen, Li

The aspect of formation and evolution of the recycled pulsar(PSR J0737-3039 A/B) is investigated, taking into account the contributions of accretion rate, radius and spin-evolution diagram(– diagram) in the double pulsar system. Accepting the spin-down age as a rough estimate(or often an upper limit) of the true age of the neutron star, we also impose the restrictions on the radius of this system. We calculate the radius of the recycled pulsar PSR J0737-3039 A ranges approximately from 8.14 to 25.74 km, and the composition of its neutron star nuclear matters is discussed in the mass-radius diagram.

Evolution of the broadband spectrum of accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2005 outburst

Ding, Guoqiang

Using the data the from RXTE satellite, we investigate the evolution of the broadband spectra (3-200 keV) of accreting millisecond X-ray pulsar (AMXP) during its 2005 outburst. With a multicomponent model consisting of a blackbody, a thermally comptonized component, a relativistic disk emission line, a multicolour disk blackbody component, and a power law, the spectra are fit statistically well. Our spectral analyses suggest that during the stages with relatively high source luminosity, the accretion disk is present and the disk resides between the neutron star (NS) and the co-rotation radius, while the disk emission disappears during the low luminosity stages. It is likely that the “propeller”effect takes place in the rapid drop stage, based on which the estimated NS surface magnetic field strength is about 108 G. During the disk accretion episodes the NS is heated and, however, it is cooling when the disk accretion stops. Comparing the spectral fitting parameter and luminosity of this AMXP with those of Z and Atoll sources, we argue that the comptonization region should be transparent to the NS emission for producing the X-ray pulsations in NS low mass X-ray binaries, and the intermediate mass accretion rate might be another requirement for generating X-ray pulsations. Type I X-ray bursts are detected during the outburst, which comforms that the compact object in this system is a NS.

Bright Merger-nova Emission Powered by Magnetic Wind from a Newborn Black Hole

Lei, Weihua

Mergers of neutron star–neutron star (NS–NS) or neutron star–black hole (NS–BH) binaries are candidate sources of gravitational waves (GWs). At least a fraction of the merger remnants should be a stellar mass BH with sub-relativistic ejecta. A collimated jet is launched via the Blandford–Znajek mechanism from the central BH to trigger a short gamma-ray burst (sGRB). At the same time, a near-isotropic wind may be driven by the Blandford–Payne mechanism (BP). In previous work, additional energy injection to the ejecta from the BP mechanism was ignored, and radioactive decay has long been thought to be the main source of the kilonova energy. We propose that the wind driven by the BP mechanism from the newborn BH’s disk can heat up and push the ejecta during the prompt emission phase or even at late times when there is fall-back accretion. Such a BP-powered merger-nova could be bright in the optical band even for a low-luminosity sGRB. We apply this model to explaine the kilo-nova in GW170817.

BH/PSR Binaries in the Galaxy

Shao, Yong

We have performed population synthesis calculation on the formation of binariescontaining a black hole (BH) and a neutron star (NS) in the Galactic disk.Some of important input parameters,  especially for the treatment of common envelopeevolution, are updated in the calculation. We have discussed the uncertainties from the starformation rate of the Galaxy and the velocity distribution of NS kickson the birthrate ($ \sim 0.6-13 \rm\, Myr^{-1}$)of BH/NS binaries. From incident BH/NS binaries, by modelling the orbital evolutionduo to gravitational wave radiation andthe NS evolution as radio pulsars, we obtain the distributions of the observable parameterssuch as the orbital period, eccentricity and pulse period of the BH/pulsar binaries.We estimate that there may be $\sim 3-80  $ BH/pulsar binaries in the Galactic disk and around10\% of them could be detected by the Five-hundred-meter Aperture Spherical radio Telescope.

2015-2016 NuSTAR monitoring of the non-thermal emission around the Arches cluster

Kuznetsova, Ekaterina

Recent NuSTAR and XMM–Newton observations of the molecular cloud around the Archescluster demonstrate a dramatic change both in morphology and intensity of the non-thermalemission, similar to that observed in the Central Molecular Zone (CMZ) of the Galactic Center(GC). Strong variations of the molecular clouds support the X-ray reflection mechanism offluorescence observed in CMZ and reveal propagation of illuminating fronts, presumablyinduced by the past flaring activity of Sgr A*. We continue monitoring campaign of the Archescluster with NuSTAR and will present results based on the recent observations, revealing thecurrent intensity level of the non-thermal emission from the molecular cloud.


Xu, Xiao-Tian

Recent years, Knigge et al. (2011) reported that there are two populations of Be/X-ray pulsars (BeXPs), which arerelated to different accretion modes (Cheng et al. 2014). In this work, we investigate the spin evolution of BeXPs bytaking into account dipole radiation, the outburst phase and the quiescent phase of the type I outburst, advection-dominated accretion flow, disk wind, and the type II outburst. We demonstrate that the type II outburst is capableof generating the population with spin period P < 40s and the observed BeXPs are in or near the spin equilibriumstate. We adopt the Markov chain Monte Carlo  method to fit our model to the observed distribution, which is well reproduced by our model with reasonable parameters. Our results implies that the outburst rate and duration of the type II outburst potentially depends on the orbital parameters, and, from the perspective of spin evolution, magnetars may exist in the population with P ~ 1000 s.

Broadband spectral study of M33 X-6 with Swift-XRT and NuSTAR: a new extragalactic Z-type source?

Nikolaeva, Svetlana

We present results of a broadband (0.3-20 keV) spectral analysis of the luminous X-ray binary system X-6 located in the nearby spiral galaxy M33. NuSTAR has measured its spectrum above 10 keV for the first time. We utilized Swift-XRT archival data to extend energy coverage to below 3 keV. The spectrum is well described by a slim accretion disk model with a maximal temperature of ~2 keV at the inner disk radius of a few kilometers. There is also evidence for an additional hard spectral component at energies above 10 keV. These results indicate that M33 X-6 may belong to the class of Z-type sources, well known in our Galaxy, in which near-critical accretion takes place on a neutron star with a low magnetic field.

Ultraluminous X-ray sources

Fabrika, Sergei

The origin of ultraluminous X-ray sources (ULXs) in external galaxies whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times is mysterious. Their X-ray spectra indicate a presence of hot winds in their accretion disks. The new results were discovered, ULX-pulsars and high-velocity outflows up to 0.2c. They are in accordance with the super-Eddington accretion. Here we analyze the variability properties of the only five ULXs which show flat-topped noise (FTN) and QPO in their X-ray power density spectra. In each ULX the mass accretion rate may vary up to 3-4 times, and with decreasing the accretion rate (reduction the spherization radius), the hardness ratio and luminosity increase, FTN and QPO may dissapear. We may potentially measure the black hole masses using X-ray luminosities. However, the strongest evidences come from optical spectroscopy. The spectra of the ULX counterparts are very similar to that of SS433 and WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state. We find that the spectra do not originate from WNL/LBV type donors but from strong winds in the accretion disks, which have similar physical conditions as the stellar winds from these stars. The results suggest that the bona-fide ULXs have supercritical accretion disks.

The formation of WR+O systems in the SMC

Chen, Wang

Wolf-Rayed (WR) stars are Hydrogen deficient on top and believed to be the late evolutionary phase of massive stars. It is proposed that binary evolution should play a vital role in the formation of WR stars in the SMC due to weak stellar wind. However observations give a similar fraction of single WR stars and WR binaries in the SMC. There are twelve WR stars observed and five of them are in binaries. Among them AB8 is the only observed WO type star. In this work we explore the formation channel for three WR binary systems AB3, AB7 and especially AB8 using MESA. We estimate tens of thousands of binary models and try to find out the probable progenitors for these WR binaries. We check the influence of semi-convection, stellar wind and binary interaction. We compare the observations with our theoretical models using least square method and Bayesian analysis. We find that all of these three WR binaries can be reproduced with our current models. They will experience non-conservative mass transfer. For AB8, we prefer efficient semi-convection that can extend He burning lifetime and can extend the convective core during He burning phase. These will help to expose Carbon and Oxygen on top. Besides we also need to increase the commonly adopted stellar wind mass loss rate during WR phase in the stellar evolutionary code in order to reproduce AB8. We found that the reproduction of the normal WN stars AB3 and AB7 are insensitive to the adopted semi-convection parameter and the stellar wind.

Mars Probe Orbit Determination with Combined OCN and XNAV

WEI, Erhu

The precise autonomous navigation for deep space exploration by combination of multi-sourceobservation data is a key issue for probe control and scientific applications. In this paper, the performance of an integrated Optical Celestial Navigation (OCN) and X-ray Pulsars AutonomousNavigation (XNAV) system is investigated for the orbit of Mars Pathfinder. Firstly, OCN andXNAV single systems are realised by an Unscented Kalman Filter (UKF). Secondly, the integrated system is simulated with a Federated Kalman Filter (FKF), which can do the informationfusion of the two subsystems of UKF and inherits the advantages of each subsystem. Thirdly,the performance of our system is evaluated by analysing the relationship between observationerrors and navigation accuracy. The results of the simulation experiments show that the biasesbetween the nominal and our calculated orbit are within 5 km in all three axes under complexerror conditions. This accuracy is also better than current ground-based techniques.

Optical Monitoring of High Mass X-ray Binary Systems with Black Hole Component

Kocak, Dolunay

We presented long term optical observations of the selected high mass X-ray binaries with black hole components. New observations obtained by using the 1m and 0.6m telescopes at the TÜBITAK National Observatory (TUG). Photometric behaviors of the systems are analyzed and compared with the earlier published results. We will discuss new observations results in this study.This study is supported by the Turkish Scientific and Research Council-TÜBITAK (117F118). We thank to TUBITAK for a partial support in using T100 and T60 telescope with project number 15AT60-775, 15CT100-916 and 17BT100-1204.

Optical variations of selected LMXB and HMXB systems with neutron star

Icli, Tugce

Long-term and short-term photometric variation of the selected LMXBs and HMXBs with neutron star component are studied. We obtained new VRI observations of the selected systems by using 60cm Robotic telescope and 100cm telescope at the TÜBITAK National Observatory (TUG). We combined all the available observations of the systems with our new observations. Long- and short period light variation are discussed in this study.This study is supported by the Turkish Scientific and Research Council-TÜBITAK (117F118). We thank to TUBITAK for a partial support in using T100 and T60 telescope with project number 15AT60-776, 15CT100-916 and 17BT100-1204.

High Resolution Spectral Analysis of SN 2011fe and SN 2014J

KIM, Soo Hyun

 We present some results of spectral analysis for Type Ia supernova SN 2011fe in M101 and SN 2014J in M82. We performed spectroscopic observations with BOAO Echelle Spectrograph (BOES) attached to 1.8-m reflector (at Yeongcheon, South Korea). Our spectra was obtained for 18 epochs in 9 nights from September 6 2011 to April 1 2012 UT for SN 2011fe and 26 epochs in 6 nights from 22 January 2014 to 23 February 2014 UT for SN 2014J. SN 2011fe shows typical Type Ia spectra. High Velocity Features (HVF) are appeared in Si II and Ca II triplet. Absence of Ha emission line on late phase spectra and asymmetric features on several absorption lines indicate possibility of double degenerate scenario. SN 2014J also shows Type Ia spectra and HVF. We find notable feature around Na I doublet lines caused by ISM. No blueshifted Na I D lines and asymmetric features, which are appeared in SN 2011fe, also indicate possibility of double degenerate scenario. Comparison between SN 2011fe and SN 2014J by spectral feature variations for several significant lines including Ca II triplet, Si II and C II will be discussed.

Optical and X-ray study of V404Cyg during its activity in the Summer 2015.

Nikolaeva, Evgeniya

We have observed optical outburst of theblack holeX-ray binary V404 Cygin Summer 2015 by using 1.5-meter Russian-Turkish optical telescope (RTT150) facilities.The velocity of shell expansion was measured basedon hydrogen and helium lines. From June 22 to June 28 2015shell expansion velocity decreased from 650 to 350 km/s as measured by Ha and Hß lines, from 450 to 300 km/s as measured by lines of HeI 6678 Å, 7065 Å and from 580 to 300 km/as measured by HeII 4685 Å line. Thus, it can be concluded the shellexpansion occurred with decelerationin the indicated period. The hydrogen and helium line formation regions in different stages of ionization are situated at different radial distances from the center of the star.The X-ray light curves of V404 Cyg were studied during its outburst activity in June and December 2015 by using open archive data of the Swift XRT orbital observatory. The power spectra constructed by using  optical and X-ray light curves showed the same slope within the error limits - -1.9 +/- 0.09 and -1.85 +/- 0.06. At frequencies from 0.002 Hz and below, a "flat area" was detected the X-ray power spectrum of V404Cyg. In the X-ray region, the power spectrum exhibits quasiperiodic oscillations at the frequency of 0.0137 Hz, its nature is unknown. It is assumed that the correlation of flow variability in the optical and X-ray ranges is caused by fluctuations in the rate of accretion near a compact source where X-ray photons are generated. X-ray photons go then  into density fluctuations in the expiring hot baryon jet radiating in the optical and X-ray ranges.

The geometric distance and binary orbit of the HMXB PSR B1259-63

Ribó, Marc

The high-mass gamma-ray binary system PSR B1259-63/LS 2883 consists of a pulsar in a 3.4-year orbit with a high-mass Oe-type companion star. Every periastron passage, multi-wavelength flaring extending up to GeV and TeV energies is seen as the pulsar moves through the disk of material surrounding its O9.5Ve stellar companion. Using the Australian Long Baseline Array we carried out a 4.4-year astrometric campaign, fully sampling the binary orbit. We measured the parallax, inclination angle of the binary orbit, and the sense of the pulsar orbit on the plane of the sky. Together with high-precision pulsar timing results, all the astrometric and orbital parameters of the system are now fully determined. In this poster, we will present our results, which are consistent with the system having formed in the Cen OB1 association and receiving a modest velocity kick in the natal supernova. We also placed constraints on the mass of the stellar companion, and confirmed that the X-ray-emitting knot seen moving away from the system Is directed along the orbital semi-major axis, towards apastron.

The search for black holes and black hole binaries using GPU accelerated supercomputers

Spurzem, Rainer

  Black Holes are difficult to detect through electromagnetic radiation alone.  Indirect evidence for their existence in our universe has been accumulated on a  large range of black hole mass scales (supermassive in galactic nuclei, stellar in X-ray binaries and most notably recently by direct gravitational wave detection through  LIGO/Virgo). Intermediate mass black holes may exist too, but remain the most  speculative variety of their kind. Recently, gravitational waves from coalescing  stellar mass black holes have been detected by the LIGO instruments. This is considered  a first direct evidence of the existence of black holes and their binaries. In our team we have been working on the interaction of black holes on all mass scales  with stellar clusters surrounding them - globular and nuclear star clusters with  stellar mass black holes and galactic nuclei with supermassive ones. We study with some of the largest possible  computer simulations (direct N-body simulations on GPU accelerated parallel supercomputers) realistic star clusters including a full stellar population (singles and binaries). Ultimately compact black hole binaries form, and with Post-Newtonian general  relativity (if needed) we follow how they evolve, disrupt stars,  and emit gravitational waves. The talk will give an overview of simulations,  methods used and results obtained. Astrophysical topics are for example the ``detection''  of black hole mergers like observed by LIGO in our N-body models; we derive the expected gravitational wave spectrum and waveforms of black hole mergers happening in our computer model and compare it to the observed ones by LIGO. The results give us (with still high uncertainties) clues about the possible origin of observed LIGO events.

SWIFT/XRT Observations of Cataclysmic Variables

Ok, Samet

Abstract            Cataclysmic variables (CVs) consist of a white dwarf that accretes matter via Roche-lobe overflow from late-type donor stars. The orbital periods of these close binaries lie between ~80 min and ~10 hours. These are WD analogues of the low-mass X-ray binaries. These systems are very important laboratories which offer enormous diagnostic power for accretion physics and allow a direct mass measurements.            CVs radiate in a wide energy range from infrared and optical bands to the hard X-rays. The main emission components in the case of the WDs with a weak magnetic field are the companion star which is a dwarf star with temperatures of 3500 - 4000, the accretion disk or accretion column near the WD surface radiating in X-rays.            In this study, we have undertaken a survey of CVs using Swift/XRT instrument to investigate their optical and X-ray luminosity relation. Such a study has been done before for dwarf novae in quiescence. In addition to this study, we used more DNe objects and also magnetic CVs.           

XXX IAU General Assembly | ACV - Austria Center Vienna  | Bruno-Kreisky-Platz 1  | 1220 Vienna