Division D - Abstracts
Introduction to Insight-HXMT: China's first X-ray Astronomy Satellite
Zhang, Shuang-Nan
Insight-HXMT is China’s first X-ray astronomy satellite launched on June 15th, 2017. It carries three sets of collimated X-ray instruments, covering energy ranges of 1-15 keV, 5-30 keV, and 20-250 keV, respectively. In addition, it can serve as a nearly all-sky monitor for high energy sources between 0.2 to 3 MeV, such as bright pulsars and gamma-ray bursts. The performance verification (PV) and calibration program has finished in November 2017 and the regular science observation program has has been on going. In this talk, I will describe the instrumentation of Insight-HXMT, its in-orbit performance and some early results, including the Galactic plane scanning survey, black holes, pulsars, gamma-ray bursts, etc.
Insights into the Fermi Bubbles from 21cm HI Observations
Lockman, Felix
The Fermi Bubbles are regions of hot gas extending many kpc above and below the Galactic center that were formed through energetic events associated with the Galactic nucleus (1). The Bubbles are traced by very faint emission across the electromagnetic spectrum implying that they contain non-thermal particles as well as hot, ~107 K thermal gas. The origin of the bubbles, as well as their energetics and lifetime, is uncertain. There are also uncertainties in the size and structure of the bubbles near the Galactic plane, where confusion with foregrounds is severe.Spectroscopic studies offer the advantage of a kinematic removal of foregrounds and the ability to trace material in the bubbles directly. In 21cm HI observations the Bubbles appear as voids in the extended HI layer (2, 3). And within these voids is a population of HI clouds apparently entrained in the outflowing nuclear wind (4). These clouds allow the Bubbles to be studied close to their source and establish limits on energetics. The Green Bank Telescope was recently used to survey the inner Galaxy for neutral clouds entrained in the nuclear wind, and has detected more than 100 such objects (5). Together with information from UV absorption lines on directions that pierce the Fermi Bubbles (e.g., 6, 7), a picture emerges which implies an outflow luminosity > 3 x 1040 ergs/sec over the last 10 Myr, and a cold-gas mass flow into the Bubbles of ~0.1 M?/yr. REFERENCES: 1. Su, M. et al. 2010, ApJ, 724, 10442. Lockman, F.J. 1984, ApJ, 283, 903. Lockman, F.J. & McClure-Griffiths, N.M. 2016, ApJ, 826, 2154. McClure-Griffiths, N.M. et al. 2013, ApJL, 770, L45. Di Teodoro, E.M. et al. 2018, ApJ (in press)6. Fox, A.J. et al. 2015, ApJ, 799, L77. Savage, B.D. et al. 2017, ApJS, 232, 25
Spectroscopic observations of the kilonova associated with GW170817
Malesani, Daniele
The rapid localization of the optical counterpart of the merging neutron star event allowed a plethora of spectroscopic observations of the highest quality, leading to the first secure identification of a kilonova. These spectra contain novel information on the explosion physics and on the composition of the ejecta, including the likely identification of r-process elements. I will review the existing studies and present the results while waiting for the forthcoming start of the LIGO/Virgo O3 observing run in late 2018.
The current status of XARM
Tashiro, Makoto
The X-ray Astronomy Recovery Mission (XARM) is planned to resume high resolution X-ray spectroscopy with imaging once realized but unexpectedly terminated by a mishap of Hitomi. JAXA and the international collaboration realizes the recovery mission focusing on large scale flows of energy and matter in the universe with the high-resolution X-ray spectroscopy. XARM carries a 6 x 6 pixelized X-ray micro-calorimeter array on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces science objectives, mission concept, project status and schedule of XARM.
The Transient Radio Universe
Kramer, Michael
Exploring the transient Universe at radio wavelengths offers a number of exciting possibilities. In contrast to most other wavelength bands, we detect a large number of photons that we can also easily digitize and manipulate. That allows us to obtain very high time resolution (nanoseconds), large fractional bandwidth (around 50% or more), and polarisation information. All of this helps in characterising the signals, or – even more exciting – discover signals of previous unknown origin, such as pulsars or recently Fast Radio Bursts. Even though the photons are of low energy, the are often produced in highly energetic processes and by compact objects. This allows us to utilize them for applications in fundamental physics, whether it is the study of gravity or super-dense matter, or cosmological applications. This talk will highlight some of the recent developments in the field, both addressing the observational aspects as well as recent discoveries and unsolved problems.
Recent results on Pulsar Wind Nebulae
Kargaltsev, Oleg
Pulsars are powerful sources of relativistic winds. The interaction with the ambient medium causes these winds to abruptly slow down, leading to the formation of pulsar wind nebulae (PWNe). These nebulae are prominent non-thermal sources seen from radio to TeV gamma-rays. To date, more than one hundred PWNe have been found in X-rays, a couple dozen in TeV gamma-rays, and about a dozen in the radio. I will review the properties of PWNe focusing on recent progress that has been made in this area. Specifically, I will talk about the PWNe of supersonically-moving pulsars where very long tails, "misaligned outflows", and UV bow shocks have been discovered. I will also present spatially-resolved spectroscopy of bright PWNe and discuss the connection between the morphologies of the PWNe and pulse profiles of their parent pulsars. Finally, I will discuss the energetics and radiative efficiencies of PWNe and the implications for the particle acceleration processes.
A Commensal Radio Astronomy FAST Survey (CRAFTS)
Li, Di
Having achieved ‘first-light’ right before the opening ceremony on September 25, 2016, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is now kept busy with commissions. We have devised a survey plan, namely, the commensal radio astronomy FAST survey (CRAFTS) to utilized the full sensitivity of FAST, while minimizing the complexities in operating the system. The 19-beam L band focal plan array will be rotated to specific angles and taking continuous data streams while the surface shape and the focal cabin stay fixed. CRAFTS will cover the northern sky in about 220 full days. In testing CRAFTS, we have already started to discover new radio counterparts to Fermi sources. Our aim is to obtain data for pulsar search, HI (neutral hydrogen) galaxies, HI imaging, and radio transients, simultaneously, through multiple backends. These data sets could be a significant contribution to all related fields and remain relevant for decades.
Recent LIGO results on Gravitational Waves
Shoemaker, David
The ground-based gravitational-wave detector network of LIGO and Virgo discovered a neutron-star binary inspiral and coalescence on 17 August 2017. This event, and a near-coincidence with a gamma ray signal from Fermi and Integral, stimulated a rapid and robust electromagnetic followup campaign which has led to rich results for astrophysics and astronomy. The properties of gravitational-wave source are inferred by matching the data with predicted waveforms based on general relativity. The gravitational-wave signal alone allowed a determination of the masses of the objects, the distance to the coalescing binary, a revised estimate of the rate of such signals, and information on the spins and tidal deformability of the neutron stars. With the associated gamma-ray burst, strong constraints are placed on the fundamental physics of gravity. Using existing redshift measurements of the host galaxy and the gravitational-wave measured distance, an independent determination of the Hubble constant is made. The source was rapidly localized to a region of 31 deg2 and the resulting sky map was issued to observing partners, allowing the identification of an electromagnetic counterpart; the consequences will be discussed in accompanying talks.
NICER: Early Operations and First Year Results
Gendreau, Keith
The Neutron Star Interior Composition Explorer (NICER) was launched in June 2017 to the International Space Station (ISS) where it is studying the transient X-ray sky. NICER consists of a collection of X-ray concentrators, silicon drift detectors, an optical bench and pointing system that provides a large collection area in the soft (0.2-12 keV) X-ray bandpass. NICER time stamps individual X-ray photons to an absolute precision of better than 100 nanoseconds while providing moderate CCD like energy resolution. Since installation, NICER has observed over 200 celestial targets including neutron stars and other celestial objects. The primary focus of NICER is to understand neutron star structure, dynamics, and energetics. We will describe the instrument, early operations, and initial results from the first year. In addition, NICER has demonstrated the use of some millisecond pulsars as navigational beacons. NICER will complete its baseline mission in January 2019. Conditional on the status of its baseline science objectives, NICER will be open to a guest observer program with first round proposals due in mid 2018 for observations beginning in 2019.
GW170817: multi-messenger observations of a binary neutron star merger
Branchesi, Marica
The detection of the first signal from the colascence of two neutron stars by the Advanced LIGO and Virgo interferometers gave rise to the largest multi-messenger observational campaign ever. The discovery of an optical counterpart in NGC4993 was followed by late X-ray and radio detections. The collected multi-messenger data confirmed theoretical models developed years ago. But at the same time, the richness of details of the data required to develop new scenarios to be interpreted. The talk will give a summary of the multi-messenger observations, intepretation and astrophysical implications.
The Imaging X-ray Polarimetry Explorer (IXPE)
weisskopf, martin
It has been over 43 years since the last extra-solar X-ray polarization observation was performed. Recently NASA selected a new, exciting mission, as part of the Small Explorer Program which will, for the first time, produce image-resolved polarimetry of astronomical sources. I am the Principal Investigator of this mission. I shall review the history of astrophysical X-ray polarimetry, discussing various experimental techniques and emphasizing the successful method of tracking the photoelectron in a low-Z gas that has allowed this experiment to proceed. After a discussion of the Observatory and its components, I shall present examples of the scientific advances that can be made by adding imaging polarimetry to the X-ray astronomer’s arsenal of tools for probing diverse questions such as: Was the black hole at the center of the Milky Way galaxy one million times more active a few hundred years ago? What is the spin the black holes in microquasars? Is there direct evidence for the effects of quantum electrodynamics in the strong magnetic fields in magnetars?
Acceleration of Cosmic Ray Electrons at Shocks in Merging Galaxy Clusters
Kang, Hyesung
Weak shocks with typical Mach number, M<3, are expected to form due to supersonic flows in merging galaxy clusters. The presence of such shocks has been indicated by X-ray and radio observations of many merging clusters. In particular, diffuse radio sources known as radio relics could be explained by synchrotron-emitting electrons accelerated via diffusive shock acceleration (Fermi I) at collisionless shocks in high-beta intracluster medium. It has been also suggested that nonthermal electrons can be further accelerated via stochastic acceleration (Fermi II) by MHD/plasma turbulence downstream of such shock. In this contribution, we explore a reaccelration model in which a shock of M=2-4 sweeps through a preshock cloud containing low-energy fossil electrons, supplemented by Fermi II acceleration due to transit time damping resonance off compressive MHD turbulence in the postshock region. We find that turbulent acceleration with tac ~108 yr is required in order to match the observed broad profiles of the radio flux density of a few radio relics.
Insight-HXMT Galactic scanning survey
Guan, Ju
The Insight-HXMT telescope launched on June 15 2017 is China's first X-ray astronomy satellite. One of its main scientific goal is to scan the Galactic Plane to find new transient sources and to monitor the known variable sources, and to observe X-ray binaries to study the dynamics and emission mechanism in strong gravitational or magnetic fields. We will detail the scanning strategy，the data processing pipeline and some interesting results in this report.
Observations of Gamma-Ray Burst (GRB) and Gravitational Wave Electromagnetic counterpart (GW EM) by Insight-HXMT
Xiong, Shaolin
The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope), the first Chinese X-ray space telescope launched on June 15, 2017, is primary designed to observe the hard X-ray sky from its narrow Field of View (~6 deg) defined by the collimators. However, thanks to the innovative usage of the anticoincidence detector, HE has been extended to monitor GRBs and GW EM counterparts, making it one of the most large gamma-ray monitors in the multi-messenger gravitational wave astronomy era. HE features a very large collection area (~1000 cm2), moderate localization accuracy (~5 deg) and microsecond time resolution in 0.2-5 MeV. As of Feb. 2018, Insight-HXMT/HE has detected more than 45 GRBs, including several short hard ones which were solely detected by it. During the observation of the first binary neutron star merger (GW170817), Insight-HXMT/HE monitored the entire GW localization area throughout the trigger time. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints (~10-7 to 10-6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger.
Failed Supernovae and Fallback Accretion
Coughlin, Eric
A failed supernova, which occurs when the core of a massive star collapses but does not produce a successful supernova, still radiates a prodigious amount of neutrinos during the de-leptonization of the iron core. These neutrinos carry with them a few tenths of a Solar mass of mass-energy, and this mass loss produces a weak shock in the outer layers of the star. I will discuss the formation and evolution of this shock, and I will demonstrate that its passage through the stellar material generates a mild explosion with a range of binding energies. I will describe a model for the dynamical evolution of the low-binding energy ejecta, and I will show that its fallback onto the black hole can power super-Eddington accretion for months to years following the initial failure of the supernova. The implications of this long-lived phase of hyperaccretion will be discussed in the context of ultra-long gamma-ray bursts and jetted tidal disruption events.
NuSTAR view of the central region of M 31
Stiele, Holger
With a distance of 780 kpc and moderate Galactic absorption, the Andromeda galaxy (M 31 or NGC 224), is an ideal target to study the X-ray source population of a nearby large spiral galaxy. NuSTAR observed the central region of M 31 in 2015 and allows studying the population of X-ray point sources at energies higher than 10 keV. Based on the source catalogue of the large XMM-Newton survey of M 31, we identified counterparts to the XMM-Newton sources in the NuSTAR data. The NuSTAR data only contain sources of a brightness comparable (or even brighter) than the selected sources that have been detected in XMM-Newton data. Here we present our investigations of hardness ratios, spectra and long-term light curves of individual sources obtained from NuSTAR data. Based on our spectral studies we suggest four sources as possible X-ray binary candidates. The long-term light curves of seven sources that have been observed more than once show low (but significant) variability.
Contribution of the Pierre Auger Observatory to the new era in multi-messenger and time-domain astronomy
García, Beatriz
Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. To study these “messengers” the Pierre Auger Observatory (PAO) is the largest facility on the Globe, with an extension of 3000 km², 1660 Surface Detectors and 27 Fluorescence Telescopes.During the last year the International Collaboration at PAO produced a series of high impact results in this field of research:1. The Observation of a Large-scale anisotropy in the arrival directions of Cosmic Rays using 3 × 10^4 events with energies above 8 × 10^18 eV from a total exposure of 76,800 km^2 sr year. The anisotropy can be well represented by a dipole with an amplitude of 6.5 (+13/-9) % in the direction of right ascension = 100° ± 10° and declination = –24 (+12/-13) °. The magnitude and direction of the anisotropy support the hypothesis of an extragalactic origin for the highest-energy cosmic rays,rather than sources within the galaxy.2. The multi-messenger observations of a binary neutron star merger, and in particular the search for ultra-high-energy neutrinos above ~ 10^17 eV using PAO Surface Detector.3. The indication of anisotropy in the arrival directions of ultra-highenergy cosmic rays through comparison to the flux pattern of extragalactic gamma-ray sources.In this contribution we will present an overview of these works, which mark a new era in multi-messenger, time-domain astronomy and demonstrate the importance of collaborative gravitational-wave, electromagnetic and neutrino observations.
A Search for X-ray Beacons in the Early Universe
Schwartz, Dan
We report on a Chandra "snapshot" survey of 14 radio quasars atredshifts z>3. These are selected to have one sided, arc-sec scalestructure, either a jet or lobe, and come from a complete, objectively-definedparent sample with radio flux density > 70 mJy in the FIRST survey, and with aspectroscopic redshift from the SSDS. Our objectives are to find X-ray emitting jets,compare the X-ray and radio morphology, and detect X-ray emissionarising from inverse Compton scattering of the cosmic microwave backgroundeven for those cases where the radio emission is no longer detectable.
X-ray transients observed by MAXI
Kawai, Nobuyuki
Monitor of All-sky X-ray Image (MAXI) on the ISS scans most of the sky every 92 minutes in the 2-30 keV band since August 2009. In the last one year since September 2017, three X-ray transients discovered by MAXI have been confirmed by follow-up observations by Neil Gehrels Swift Observatory and ground-based telescopes, including two black hole candidates MAXI J1535-571 and MAXI J1813-095. We searched for X-ray counterparts of gravitational wave sources including the neutron star merger GW170817 for which we provided the earliest X-ray upper limit. MAXI also provided long-term X-ray light curves for numerous X-ray sources. For some bright sources, the variation of energy spectra associated with state transitions can be studied. We present the results from the long-term monitoring of GRS 1915+105, and compare with past pointed observations.
Multi-epoch observations of the Blazar 1ES2344+514 using ASTROSAT, GMRT, Fermi and WEBT
Shastri, Prajval
1ES2344+514 is a blazar discovered by the Einstein Observatory and first found by the Whipple Observatory to have gamma-ray emission. It is known to be highly variable at all frequencies observed so far and on multiple time-scales, consistent with the expectation for blazars. The SEDs previously derived from the available sparse data have been shown to be broadly consistent with a synchrotron self-Compton model. During 2016 we observed 1ES2344+514 with the hard X-ray (LAXPC), soft X-ray (SXT) and ultraviolet (UVIT) telescopes on ASTROSAT at four epochs, and at radio wavelengths with the GMRT at one of these epochs with a cadence of about a month. We observed a brightening of the blazar at one of the epochs. We use these data and quasi-simultaneous WEBT observations to infer the Spectral Energy Distribution for the blazar.
Superstrong B-fields of neutron stars in Be XRBs
Shi, ChangSheng
We re-estimate the surface magnetic fields of neutron stars (NSs) in Be X-ray binaries (BeXBs) with different_x000D_ models of torque. In particular, a new torque model is applied to three models of magnetosphere radius. Unlike the previous models, the new torque model does not lead to divergent results for any fastness parameter. The inferred surface magnetic fields of these NSs for the two compressed magnetosphere models are much higher than that for the uncompressed magnetosphere model. The estimated surface magnetic fields for NSs BeXBs in the Large Magellanic Cloud, the Small Magellanic Cloud and the Milk Way are between the quantum critical field and the maximum “virial” value by the spin equilibrium condition.
Quantum electrodynamics mechanisms in the pulsar magnetosphere: synchrocurvature radiation and γγ->e+e- pairs
Voisin, Guillaume
It was shown as soon as 1969 that the pulsar magnetosphere must have vacuum gaps, where intense electric fields developthat are capable of accelerating the rarefied plasma to very high energies along the magnetic field. The curvature of the field lines, together with the rotation around the magnetic field, results in the so-called « synchrocurvature » radiation. The energy is mostly radiated in gamma photons (γ). These photons may then be converted by the γ-photon magnetic-field or γ-γ quantum processes in an electron-positron pair e+e-, each component of which then radiates at its turn which results in a cascade that provides plasma to the magnetosphere. In this talk, I focus on two key phenomena of these cascades : synchrocurvature radiation and γγ->e+e- pairs. How to quantify synchrocurvature radiation? What is the impact of the strong anisotropies in the background x-ray photon field involved in the γγ pair production mechanism? On the one hand, we will see that the effects of quantifying synchrocurvature radiation can be very important in pulsar magnetopsheres, leading to qualitatively different gamma-ray spectra. On the other hand, we will present a formalism simultaneously accounting for the energy and angular distribution of outgoing leptons for an arbitrary photon background in the γγ->e+e- process, and see what role this may play in a detailed modeling of the pair cascade.