Location: King Henry 0.01

P1 - Monday 14:00-15:40 (Paolo D'Avanzo)

Formation and Galactic Distribution of Black Hole X-ray Binaries with Gaia DR2


Anjali Rao (Physics and Astronomy, University of Southampton)

Astrometry of black hole X-ray binaries (BHXBs) provide significant empirical support in developing the understanding of the formation scenarios and fundamental properties of black hole X-ray binaries (BHXBs), which is of prime importance in the study of massive stellar evolution. But, their astrometric properties have been reported for a handful of objects, because their transient behavior, faint optical counterparts and large distances (> 1 kpc) have made comprehensive astrometric investigations of BHXBs very challenging. Gaia has dramatically changed this situation. We present distance and peculiar motion results for 11 BHXBs using Gaia DR2, with peculiar velocities for 7 of them being reported for the first time. Our results on the observed weak anti-correlation between the kinetic energy of peculiar motion and BH mass suggests a BH formation scenario where the natal kick imparted to the black hole during core collapse scales with its mass. This result is important in the light of simulation results suggesting the change in the observed Gravitational Wave merger events as a function of natal kicks. We will discuss the formation of BHXBs, particularly focusing on short orbital period systems, based on our investigation of their z-heights from the Galactic plane and their orbital period distribution. We further utilized Gaia data of Cyg X-1 to investigate its origin in the neighboring region Cyg OB3. The consistent values of distance, proper motion, peculiar and relative velocity of Cyg X-1 and those of the other stars in the region suggests that Cyg OB3 can be identified as the parent stellar association of Cyg X-1. With the present and forthcoming data releases, Gaia has emerged as a powerful aide in probing the properties of BHXBs.

On the spin of the neutron stars in wind-fed high mass X-ray binaries


Shigeyuku Karino (Science and Engineering, Kyushu Sangyo University)

We have constructed a binary evolution code which solves the evolution of NS magnetic field and spin.
With this code, we investigate the mass transfer rate from the donor to the NS via stellar wind, and trace the resultant evolution of binary parameters.
In the spin evolution of the NS, we consider variety of spin-up/down effects, including mass accretion, magnetic dipole radiation, propeller effect, and interaction with subsonic accretion shell.
Through the computations, we try to identify the origin of broad distribution of NS spins in wind-fed X-ray binary systems.
Especially, we found that, to reproduce the most slowly rotating NSs with longer spin-periods than 1,000sec, subsonic shell formation could play an important role.

The disk-reflection spectroscopy of black-hole X-ray binaries using AstroSat, Swift and NuSTAR


Sunil Chandra (Center for Space Research, North West University Potchefstroom Campus)

The disk reflection spectroscopic techniques in recent times, have become an effective methods to determine the spin of black holes, largely aided by the accessibility to  broad energy ranges of relatively modern X-ray missions namely AstroSat, NuSTAR, and the Neil Gehrels Swift Observatory (either individually or in combination). Theoretical and computational advancements in the field such as proper accounting of reflection based features along-with the prescriptions of relativistic effects and algorithms to trace back each and every photons have also been instrumental in strengthening the grounds for using this method.
However, the estimations of spin and other disk parameters (ionization, inner disk truncation, etc.) can be plagued by minor uncertainties in instrument/cross-instrument calibrations.  On the brighter side, the extensive calibration campaigns organized by IACHEC over past few years have enabled us with unprecedented simultaneous data (XMM, NuSTAR, AstroSat, Chandra, and Swift), which have led to improvements in the cross-instrument calibrations to very comfortable levels.
Our small group is involved in investigating a sub-sample of BHXRBs using publicly available data from the aforementioned observatories, and the latest reflection models distributed with XSPEC, and separately. We have recently published our reflection studies on GRS 1716-249 and MAXI J1535-571, which were observed extensively during their extended outbursts in 2017. In these works, we have also demonstrated the prospects of SXT and LAXPC instruments aboard AstroSat in performing X-ray reflection studies, in the wake of current status of cross calibrations.

Here, I intend to use this session of “Texas symposium 2019” to discuss the current updates from our studies.



Bari Maqbool (Astrophysics, Inter University Centre for Astronomy and Astrophysics, Pune India)

We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray
Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat, when the
source was in the hard spectral state as revealed by the broad-band spectra. The spectra obtained
from all the observations can be described by a single-temperature Comptonizing region with
disc and reflection components. The event mode data from LAXPC provides unprecedented
energy dependent fractional root mean square (rms) and time-lag at different frequencies which
we fit with empirical functions. We invoke a fluctuation propagation model for a simple
geometry of a truncated disc with a hot inner region. Unlike other propagation models, the hard
X-ray emission (>4 keV) is assumed to be from the hot inner disc by a single-temperature
thermal Comptonization process. The fluctuations first cause a variation in the temperature of the
truncated disc and then the temperature of the inner disc after a frequency dependent time delay.
We find that the model can explain the energy dependent rms and time-lag at different

P2 - Monday 16:10-17:50 (Paolo D'Avanzo)

Discovery of a 70-solar-mass dark object in a spectroscopic binary system


Roberto Soria (NAOC, University of the Chinese Academy of Sciences)

Stellar-mass Galactic black holes with dynamically measured masses (typically, around 5 to 15 solar masses) are all selected from a subsample of X-ray binaries with suitable outburst properties. They may not represent an unbiased sample of the mass range of stellar remnants in the Milky Way. To address this problem, we are conducting an optical spectroscopic survey of moderately bright Galactic stars (V ~ 10-13 mag) with the 4-m LAMOST telescope, looking for single-lined binaries (ie, systems where a star is orbiting a dark object). The most interesting result of our survey so far is a wide binary system (period of 78.9 days) in which an ~8 solar-mass star (stellar type B3, brightness V ~ 11.5 mag) is orbiting a dark mass of M = 68^{+11}_{-13} solar masses. The masses of the two components are calculated with standard spectroscopic techniques, from the radial velocity amplitudes of the absorption lines (tracing the stellar motion) and of a disk-like Halpha emission line (tracing the orbital motion of the dark companion, in anti-phase with the stellar motion). What is the 68-solar-mass dark object? Commonly accepted binary evolution models do not predict the formation of such massive remnants from individual stars at solar metallicity: could the models be wrong? Alternatively, the dark mass could be a tight binary system of two stellar black holes below 35 solar masses, and the B3 star could be the hierarchical third body in the system. The existence of “heavy” black hole binaries in this mass range was proved by LIGO; this Galactic system would be the first pre-merger detection of such objects, right in our backyard (only 4 kpc away). Confirming the existence and estimating the total number of such objects in the Milky Way has significant implications for theories of stellar evolution, for models of dark matter in galactic halos, and for the predicted LIGO event rate.

The past activity of Sgr A*: quantitative evidence for at least two powerful outbursts in the last 300 years


Dimitri Chuard (CNRS/APC/CEA)

X-rays emitted by Sgr A* reflect onto the giant molecular clouds populating the central molecular zone (CMZ). This gives rise to light echoes from which the bygone activity of the Galactic supermassive black hole can be retraced. However, the number of past outbursts, as well as their ages and durations, is unclear, since the line-of-sight positions of the clouds are very poorly known. Thanks to a detailed analysis of the XMM-Newton and Chandra observations of the CMZ, based on the comparison of observed spectra with Monte Carlo simulations, we succeed in placing constraints on the line-of-sight positions of eight illuminated clumps from the four main CMZ complexes, providing at the same time an estimation of the outburst ages. This analysis allows us to find with significance above 5 sigma that at least two powerful (a million times the present quiescent luminosity in X-rays) outbursts are currently propagating though the CMZ: a short one (~1 yr) generated about 85 yr ago and a longer one (~20 yr) emitted by Sgr A* about 240 yr back. This method paves the way for a detailed reconstruction of the past light curve of Sgr A* over the past millennium.

Large-scale X-ray structure of the Vela pulsar wind nebula revealed by Suzaku/XIS


Satoru Katsuda (Department of Physics, Saitama University)

In Katsuda et al. 2011, we serendipitously found diffuse hard X-ray emission just outside Vela X, a 2 degrees x 3 degrees radio pulsar wind nebula (PWN) in the Vela supernova remnant. The hard X-ray spectra were well represented by a power-law with a photon index of about 2.4, similar to that of the southern outer part of Vela X. The power-law flux decreases with increasing distance from the pulsar. These properties led us to propose that the hard X-ray emission is associated with the Vela PWN. To reveal the whole X-ray structure of the Vela PWN, we have carried out mapping observations with Suzaku/XIS. The pointings extend along four arms from near the Vela pulsar towards the north, northeast, east, and west, out to roughly 2 degrees (4 degrees in diameter). We detect hard, power-law type X-ray emission from all the fields of view. The X-ray flux decreases with increasing distance from the pulsar to the outermost pointings down near to the local cosmic X-ray background level. The morphology seems to be symmetric, which is in stark contrast to asymmetric Vela X. The X-ray spectra soften from the pulsar to outer regions (photon index of about 3.5 at maximum). We discuss the formation mechanism of the largely extended X-ray PWN.

X-ray transients hidden in the X-ray catalogs


Jonathan Quirola (Institute of Astrophysics, Pontificia Universidad Católica de Chile)

The event GW170817 was the first detection of a merger of neutron stars by the LIGO and VIRGO collaboration (LVC), and immediately it was detected for~70 observatories around the world from radio to gamma rays. GW170817 answered a fan of open questions, such as the progenitor of short gamma-ray burst (sGRBs), the r-process in the nucleosynthesis process, the first detection of a kilonovae (kNe), a new way to measure the Hubble constant using standard sirens, and the equation of state of compact objects, etc. This merger of neutron stars has begun a new era in multi-messenger astronomy. Furthermore, Bauer et. al (2017) and Xue et al. (2019), identified a new type of faint X-ray transients located in the South Chandra Deep Field (CDF-S) using X-ray Chandra data. The events were called XT1 and XT2, respectively. XT1 shows an unknown nature, although several scenarios could explain its properties such as the shock breakout from core-collapse supernovae (CCSNe), tidal disruption event (TDE) due to an intermediate massive black hole (IMBH), or an off-axis sGRB. On the other hand, XT2 is feed by a magnetar wind due to the merger of neutron stars. XT1 and XT2 are apparently related to GW170817-like events and their X-ray counterparts. Similar X-ray transients could enable us to characterize the possible neutron stars mergers detection by current LVC campaign (O3) running from April 2019. In this presentation, I will talk about a deep search of XT1 and XT2-like events using the whole Chandra Source Catalog (CSC), a database with ~300.000 sources, as well as a
comparison with optical, infrared and radio catalogs. I will present methods, sources detected, the most relevant results, implications, and relation with possible extragalactic origins.

P3 - Tuesday 14:00-15:40 (Anna Franckowiak)

Status and Prospects of Mediterranean Neutrino Telescopes: KM3NeT & ANTARES


Agustín Sánchez Losa (KM3NeT, INFN – Sezione di Bari)

For more than 10 years, the ANTARES detector has been the largest neutrino telescope in the Northen Hemisphere. By now, the construction for the significantly larger KM3NeT detector has started, with currently 5 lines operating in the Sea. KM3NeT includes two projects. KM3NeT/ORCA, offshore the French coast of Toulon, is optimized for measurements with a low energy threshold (at few GeVs) in order to perform atmospheric neutrino oscillation studies. KM3NeT/ARCA, offshore the Sicilian coast of Capo Passero, aims to surpass the km³ volume in order to perform cosmic neutrino astronomy (mainly in the TeV-PeV range). Due to its location, it has an optimal view of the Southern sky, including the Galactic Center, and it will operate with an unprecedented angular resolution and sensitivity. The latest results from ANTARES and from the first KM3NeT data, together with status and plans of the experiments, will be presented.

Ten Years of Neutrino Point-Source Searches with IceCube


Tessa Carver (Gravitational Physics, Cardiff University)

In the field of high energy astrophysics it remains to be confirmed which objects and processes are responsible for the production of ultra high energy cosmic ray events. Astrophysical neutrinos are expected as a product of hadronic interactions of these cosmic rays and therefore should indicate their relevant sources. Despite the discovery of a diffuse astrophysical flux and evidence for the blazar TXS 0506+056 as a flaring neutrino source, no steady state astrophysical neutrino source has yet been identified.
Over 10 years IceCube has continuously monitored the entire sky and extracted a selection of events optimized for neutrino point-like source analyses. We present an update on neutrino point source searches that adds 3 years of data over previous results. The final years of this dataset were implemented with a new event selection and direction reconstruction that demonstrates a more precise angular resolution leading to an improved point source sensitivity by 30% with the additional years of data. The presented analysis results include : (i) an all sky scan with no prior knowledge on the source position or spectra, (ii) an updated source catalog of candidates motivated by the latest Gamma ray observations and (iii) stacking events in the directions of different objects in updated Galactic Catalogs.

The IceCube Realtime Alert Stream


Robert Stein (DESY Zeuthen)

The IceCube Neutrino Observatory, buried within glacier ice at the South Pole, is the world’s largest neutrino telescope. Since the discovery of an astrophysical neutrino flux by IceCube in 2013, there has been an ongoing search to identify the origin of these high-energy neutrinos. The IceCube Realtime Alert Stream, first implemented in 2016, identifies likely-astrophysical neutrinos with low latency, and rapidly distributes this information to astronomers via GCN notices. One neutrino alert, IC170922A, was found to have arrived in spatial and temporal coincidence with the flaring blazar TXS 0506+056, at 3 sigma significance. I will outline the current operation of the realtime system, and highlight recent results from follow-up campaigns.

Photohadronic modelling of the 2010 gamma-ray flare from Markarian 421


Alberto Rosales de Leon (Physics, Durham University)

Blazars are a subclass of active galactic nuclei (AGN) that have a relativistic jet with a small viewing angle towards the observer. These objects have a substantial variability spectrum and can undergo flaring states, periods of enhanced activity with scales from hours to months. After a possible time correlated neutrino and gamma-ray detection coming from the blazar TXS 0506-056, hadronic scenarios have motivated an ongoing discussion of how a blazar can produce this result and which model (or models) can successfully describe the observed behaviour. Markarian 421 (Mrk 421) is one of the closest and brightest objects in the extragalactic very high energy sky (E > 100 GeV). This object showed flaring activity during a 13 day period in March 2010. Extensive data were collected from observations and provided a unique opportunity to study the temporal evolution of the SED during a flaring period. In this work we performed a Fermi analysis of the source and then apply the photohadronic model to fit the high energy gamma-ray data, the observed behaviour was interpreted in terms of a hadronic scenario.

P4 - Tuesday 16:10-17:50 (Anna Franckowiak)

A cosmic collider: Was IceCube neutrino generated in a precessing jet-jet interaction in TXS 0506+056?


Silke Britzen (Max-Planck-Institut für Radioastronomie)

The neutrino event IceCube-170922A appears to originate from the BL Lac object TXS 0506+056.
Other BL Lac objects show properties similar to those of TXS 0506+056, such as multiwavelength variability or a curved jet.
However, to date only TXS 0506+056 has been identified as neutrino emitter.
To understand the neutrino creation process and to localize the emission site, we studied radio images of the jet at 15 GHz.
Our results suggest that we observe the interaction between jet features that cross each other’s paths in TXS 0506+056.
We propose that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino
IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings seem capable of explaining the neutrino generation at the time of a low gamma-ray flux and also indicate that TXS 0506+056 might be an atypical blazar. It seems to be the first time that a potential collision of two jets on parsec scales has been reported and
that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.

Understanding the orphan neutrino flare from blazar TXS 0506+056


Xavier Rodrigues (IceCube, DESY Zeuthen)

On September 22, 2017, the first non-stellar cosmic neutrino source was identified when IceCube detected a high-energy muon neutrino from the direction of blazar TXS 0506+056. Meanwhile the source was undergoing a major electromagnetic flare. This coincidence has been well modeled by protons interacting with photons in the jet of the source, suggesting this blazar as a high-energy cosmic ray source. By analysing the archival data from the same source, IceCube also found an excess of 13+/-5 neutrinos above background in 2014/15. That signal, however, was not accompanied by enhanced electromagnetic activity, which poses a challenge to traditional models. We here use a self-consistent time-dependent numerical code previously deployed to model the 2017 flare, and make an extensive parameter space scan. We conclude that the orphan neutrino flare cannot be modeled assuming any simple geometry, but only by invoking additional structures to the jet, where cosmic-ray protons can interact with re-processed radiation from a bright accretion disk. Such a scenario gained further support by recent observations. We found that those external radiation fields, which are insignificant in the observer frame, play in fact a dominant role in producing the orphan neutrino flare.

Exploring 3D core-collapse supernovae through neutrinos


Laurie Walk (Niels Bohr International Academy , Niels Bohr Institute )

Due to their weakly interacting nature, neutrinos can be powerful probes of astrophysical environments, providing key insights into otherwise unobservable physics. For instance, neutrinos are perhaps the most essential messengers of core-collapse supernovae. These energetic stellar explosions are amongst the brightest objects in the night sky, and yet, our understanding of them remains limited. Neutrinos are abundantly produced deep inside the core of core-collapse supernovae, and they play an important role in the delayed neutrino-driven explosion mechanism; the process in which the shock wave stalls within the iron core, and is revived through neutrino heating. Closely mirroring the hydrodynamics of the explosion, neutrinos carry information  as they propagate to Earth. In this talk I will focus on how we can use state-of-the-art 3D simulations of core-collapse supernovae to identify unique signatures of hydrodynamical instabilities in the predicted neutrino signal, constrain the properties of a progenitor before the onset of the explosion, as well as characterise its final compact remnant.

P5 - Wednesday 14:00-15:40 (Paolo D'Avanzo)

Two years of Non-Thermal Emission from GW170817


Aprajita Hajela (Physics and Astronomy, Northwestern University)

GW170817 marked the beginning of the era of multi-messenger astronomy on August 17, 2017, and for the first time connected the origin of short gamma-ray burst to binary neutron star mergers. Two years later we have a consensus on a model with a structured jet that is viewed off-axis that best describes the non-thermal emission observed from GW170817 across multiple wavelengths. The energetics and microphysical parameters of the outflow model however, have a broad distribution and a high correlation. The lack of evidence of any spectral evolution in the GRB afterglow motivates us to find new ways to break the degeneracy between the afterglow model parameters, like the energy of the jet and the density of the surrounding medium. I will present a new method we developed to independently constrain the ambient density of the medium in which the outflow is expanding, to get tighter constraints on the energetics of the outflow. I will further show the inferences we draw from the two years of extensive X-ray and Radio observations of GW170817 and how we used them to put the first-ever constraints on the fastest moving Kilonova ejecta. I will also present a temporal analysis we performed to test short time-scale variability to constrain the nature of the end product of the merger.

The structure of Gamma Ray Bursts: beyond GRB 170817


Paz Beniamini (California institute of technology)

Motivated by GW170817 we examine three independent constraints on the angular structure of gamma-ray burst (GRB) jets that are required by observations of cosmological long GRBs. We find that efficient gamma-ray emission has to be restricted to material with Lorentz factor > 50 and is most likely confined to a narrow region around the core. Comparing GRB 170817 with the regular population of short GRBs (sGRBs), we show that an order unity fraction of neutron star mergers result in sGRB jets that break out of the surrounding ejecta, that their luminosity function must be intrinsically peaked and that sGRB jets are typically narrow with opening angles ~ 0.1 rad. Finally, we present new analytical modelling of GRB afterglows viewed off-axis and discuss the possible light-curves that may be seen in future GW-detected GRBs and which of their underlying physical properties can be robustly determined from observations.

GRB Structured Jets At All Angles


Geoffrey Ryan (Astronomy, University of Maryland)

Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated by the afterglow of GW170817, this requires a radical extension of the common GRB afterglow models which typically assume emission from an on-axis top hat jet. We present a characterization of the afterglows arising from structured jets, providing a framework covering both successful and choked jets. We find new closure relations for off-axis structured jets, the slope of the light curve is found to be a simple function of the viewing angle. We also present our new public GRB afterglow modelling package: afterglowpy.

Unveiling the central engine and jet structure of gamma-ray bursts with X-ray observations


Maria Grazia Bernardini (INAF, Osservatorio Astronomico di Brera)

With its rapid-response capability, Swift has given unprecedented insights on Gamma-ray bursts (GRBs), revealing an unforeseen richness in their properties in the X-ray energy band. In particular, the presence of a plateau phase and of flares in the X-ray light curve of GRBs concur with the central engine being active over a much longer timescale than the prompt phase. We review the main observational features discovered by Swift, and we discuss how they provide compelling though indirect evidences supporting the magnetar central engine for GRBs. X-ray observations have also been proven crucial in probing the GRB emission geometry in the remarkable case of GRB 170817A, the first electromagnetic counterpart of a gravitational wave event detected by the LIGO/Virgo interferometers and originated by the coalescence of a double neutron star system (GW 170817). We show how the extensive follow-up campaign carried out over two years provided clear evidence for a successful jet endowed with an angular energy profile, featuring a narrow and energetic core (seen off-axis), surrounded by a slower, less energetic layer/sheath/cocoon.

X-ray plateaus in GRBs’ light-curves from jets viewed slightly off axis


Raphaël Duque (Institut d’Astrophysique de Paris)

The X-ray light-curves of gamma-ray burst afterglows commonly
feature phases of shallowly-decaying or constant flux lasting from
hundreds of seconds to a day, known as plateaus. Correlations exist
between observable properties of the plateau and of the prompt emission for
bursts with plateaus. Over the years, the origin of these plateaus has
been tentatively traced to various mechanisms, the most discussed being
late energy injection into the forward shock. These models may reproduce
observed correlations, but their physical motivation remains elusive, in
particular with respect to the burst’s central engine activity.
We show that X-ray plateaus can occur due to purely
geometrical effects and that the observed correlations naturally arise
from these, provided the burst’s jet is laterally structured and viewed
with an angle close to its core. Recent gamma-ray burst science has
robustly shown that the two latter conditions are most often fulfilled.
We illustrate our work by comparing simulated to observed X-ray
light-curves, and study other consequences of our interpretation of
these plateaus.

P6 - Wednesday 16:10-17:50 (Paolo D'Avanzo)

GRB afterglow X-ray flares as de-boosted prompt pulses


Robert Mochkovitch (Institut d’Astrophysique de Paris)

X-ray flares are fast-rising and -decaying episodes of
order-of-magnitude rebrightening observed in a third of gamma-ray burst
afterglows. Their spectral and temporal properties recall those of
the prompt emission, which has motivated many to trace their origin to
late-time activity of the burst’s central engine.
We show here that due to geometrical effects, pulses occurring during the
prompt phase can be observed as flares in the X-ray band for an observer
placed slightly outside of the burst’s outflow’s core.
We illustrate our work by comparing observed and simulated afterglow
light-curves of on- and off-axis lines-of-sight, and study other
consequences of our interpretation for the X-ray flares.

Short Gamma Ray Bursts do they follow the star formation rate?


Maria Giovanna Dainotti (Astronomical Observatory, Jagiellonian University)

Possibly originating from neutron star-neutron star {bf(NS-NS)} mergers or black hole-neturon star {bf(BH-NS)} mergers, short GRBs {bf(SGRBs)} were the first events with associated gravitational wave observations. This association began a new era of multi-messenger astrophysics. Many recent papers in this field detail the cosmological distribution and evolution of the more numerous long GRBs {bf (LGRBs)}. However, a critical issue needs to be solved for SGRBs: the identity of the true SGRB rate and whether or not this rate follows the star formation rate {bf(SFR)}. Once we know the true SGRB rate, we can more precisely compute the expected number of SGRBs with associated graviational waves {bf(GWs)}. In this paper, we present a new determination of the luminosity and formation rate evolution of SGRBs using data from {it Swift} with non-parametric and non-binning methods from Efron & Petrosian. These methods can readily combine samples with varied selection processes and are more powerful than the usual forward-fitting methods, especially for our sample which included a small number of sources. We assumed short with extended emission {bf(SEE)} and short GRBs descend from the same progenitor, thus we considered both samples together. To avoid the incompleteness of GRB samples due to unknown $z$ we reduced the number of GRBs in our sample, allowing a relation to the parent group at the level of 89.9$%$ in flux. Our results showed short GRBs have their formation rate evolution which does not match the GRB formation rate.

Synchrotron radiation of GRB 190114C afterglow within BdHN model


MILE KARLICA (ICRANet, Sapienza University of Rome)

Gamma-ray burst (GRB) within the paradigm of the binary driven hypernova (BdHN) clearly points to its mildly relativistic regime during afterglow phase which is confirmed by early X-ray thermal component measurements around 100 seconds and optical emission lines measurement around $10^6$ seconds. Radiation in optical and X-ray band of the GRB afterglow within this paradigm come from the synchrotron radiation of relativistic electrons inside hypernova (HN) ejecta mainly magnetised by a newly created neutron star ($nu$NS). To model the temporal behaviour of the GRB afterglow spectra we have developed a kinetic equation code which tracks the evoultion of injected electrons inside HN ejecta taking into account all the important energy losses and their temporal dependence. In this talk we present the basic physical elements of our code and the relevant results for GRB130427A, GRB160625B and GRB 190114C as a clear example.

From X-Calibur to XL-Calibur – advancing balloon-borne hard X-ray polarimetry


Mark Pearce (Dept. of Physics, KTH )

Black hole binaries, neutron stars, and other compact objects are too small and distant to be imaged. Information on source geometry and high-energy emission mechanisms is instead derived from spectral and timing measurements. Results are often model dependent with interpretation subject to degeneracies which cannot be resolved. X-ray polarimetry provides a valuable independent source diagnostic. Characterising the source emission with two additional observables, the linear polarisation fraction and the linear polarisation angle disentangles geometrical and physical effects, thereby opening a new window on the high-energy universe. Only a few reliable observations of the brightest celestial X-ray sources have been made to date. Future satellite missions stand to open an observation window with unprecedented sensitivity for the classic X-ray astronomy energy range centred around a few keV. Stratospheric ballooning platforms offer an attractive way to make headway in the hard X-ray (>15 keV) regime. The XL-Calibur mission is a continuation of the X-Calibur mission which has conducted several test flights, culminating in observations of the accreting X-ray pulsar GX 301-2 during a flight on Antarctica in December 2018. XL-Calibur is a second-generation instrument which achieves approximately six times better sensitivity than X-Calibur due to several improvements. Most importantly, the 8 m long optical bench and the InFOCS X-ray mirror will be replaced by a 12 m long optical bench and the spare mirror of the hard X-ray telescope of the FFAST mission. The mirror provides an approximately four times larger effective area than the InFOCS mirror in the key energy range from 15-40 keV and an even larger improvement at higher energies. Furthermore, modifications of the polarimeter and the anticoincidence shield will reduce the background by a factor of approximately two. XL-Calibur will study a sample of archetypical X-ray sources (15-80 keV), including but not limited to, stellar mass black holes in X-ray binaries such as Cyg X-1 and GX 339-4, accretion and rotation powered neutron stars such as Her X-1, Vela X-1, GX 301-2, and the Crab, as well as a sample of flaring binaries. Simultaneous observations between XL-Calibur and the Imaging X-ray Polarimetry Explorer (IXPE) mission are foreseen, allowing the polarization of different emission components to be distinguished.