We calculate the high energy afterglow emission from short Gamma-Ray Bursts (SGRBs) in the external shock model. There are two possible components contributing to the high energy afterglow: the electron synchrotron emission and the synchrotron self-Compton (SSC) emission. We find that for typical parameter values of SGRBs, the early high-energy afterglow emission in 10 MeV-10 GeV is dominated by the synchrotron emission. For a burst occurring at redshift z =0.1, the high-energy emission can be detectable by Fermi LAT if the blast wave has an energy E>=10^51 ergs and the fraction of energy in electrons is ε_e>=0.1 . This provides a possible explanation for the high energy tail of SGRB 081024B.
We analyzed 199 GRBs detected by Fermi-LAT during the years 2008-2019. We found 67 photons at energies >=10 GeV, which come from 34 GRBs. Out of these 34 GRBs, Fermi-LAT detects significant (TS>=4) afterglow 0.1-200 GeV photons from 25 GRBs. We present time-integrated 0.1-200 GeV spectra of these 25 GRBs. The spectra of a significant fraction (9/25) of these GRBs revealed a harder component above an energy break of 0.3-2 GeV. While shock synchrotron may account for the photons at the lower energy end, high energy photons above the break is naturally explained by synchrotron self-Compton (SSC) …
The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born pulsar.
Gamma-ray bursts (GRBs) are ultra-relativistic collimated outflows, which emit synchrotron radiation throughout the entire electromagnetic spectrum when they interact with their environment. This afterglow emission enables us to probe the dynamics of relativistic blast waves, the microphysics of shock acceleration, and environments of GRBs. We perform Bayesian inference on a sample of GRB afterglow data sets consisting of 22 long GRBs and 4 short GRBs, using the afterglow model "scalefit", which is based on 2D relativistic hydrodynamic simulations. We make use of Gaussian processes to account …
We systematically investigate the outflow structure of GW170817 in comparison with a sample of 27 cosmological short GRBs by modelling their afterglow light curves. We find that cosmological short GRBs share the same outflow structures with GW170817, relativistic structured jets. The jet opening angle of GW170817 is $6.3^{+1.1}_{-0.6}{}^{\circ}$, which is consistent with that of cosmological short GRBs ($θ_0 = 6.9^\circ \pm 2.3^{\circ}$). Our analysis indicates that GW170817 is viewed off-axis ($θ_{\rm obs} = 30^{+7}_{-4}{}^{\circ}$), while cosmological short GRBs are viewed on-axis ($θ_{\rm o…
The afterglow emission from gamma-ray bursts (GRBs) is a valuable source of information to understand the physics of these energetic explosions. The blast wave model has become the standard to describe the evolution of the afterglow emission over time and frequency. Thanks to recent developments in the theory of afterglows and numerical simulations of relativistic outflows, we are able to model the afterglow emission with realistic dynamics and radiative processes. Although the models agree with observations remarkably well, the afterglow emission still contains additional physics, instrumenta…
The Swift satellite has observed more than a thousand GRBs with X-ray data. Almost a third of them have redshift measurement, too. Here we start to investigate the X-ray spectral fitting of the data considering the low energy part where the N(H) absorption happens. Based on the available more accurate input data we examined the robustness of previous fittings and tested how sensitive the changes of the starting parameters are. We studied the change of the intrinsic hydrogen column density during the outburst for a few events. No significant variability of N(H) column density was identified.
Bimodal spectral energy distributions (SEDs) of gamma-ray burst (GRB) afterglow of GRBs 190114C, 130427A and 180720B confirm that they are originated from the synchrotron emission (Syn) and synchrotron self-Compton Scattering process (SSC) of electrons accelerated in the jets. The radiation mechanism and the physics of the observed spectrum-luminosity/energy relations of GRBs remain as open questions. By extracting the Syn component through fitting their early afterglow SEDs with the Syn+SSC model, we find that their luminosity ($L_{\rm syn}$), peak energy ($E_{\rm p,syn,z}$), and the Lorentz …
The VHE component from at least two GRBs, i.e., GRB180720B and GRB190114C, has been detected in the afterglow phase. We systematically analyzed 199 GRBs detected by Fermi-LAT during 2008-2019. If an additional high-energy component exists in the afterglows of Fermi-LAT GRBs, the best-fit spectral model could be a broken power-law (BPL) model with an upturn above a break energy. We compare the afterglow spectra using PL and BPL representations. Out of the 30 GRBs with >10GeV photons that arrived after T90, 25 GRBs are tentatively or significantly detected at 0.1-200 GeV after 2*T90. The spectru…
Measuring gamma-ray burst (GRB) properties in their rest-frame is crucial to understand the physics at work in gamma-ray bursts. This can only be done for GRBs with known redshift. Since redshifts are usually measured from the optical spectrum of the afterglow, correlations between prompt and afterglow emissions may introduce biases in the distribution of rest-frame properties of the prompt emission. Our analysis is based on a sample of 90 GRBs with good optical follow-up and well measured prompt emission. 76 of them have a measure of redshift and 14 have no redshift. We estimate their optical…
Detection of afterglow emission up to 100 GeV through a stacking analysis of gamma-ray bursts
Yunnan University（云南大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；University of Science and Technology of China（中国科学技术大学）；University of Chinese Academy of Sciences（中国科学院大学）；TIANFU Cosmic Ray Research Center（天府宇宙线研究中心）；Beijing Normal University（北京师范大学）；The Hong Kong Institute for Astronomy and Astrophysics, University of Hong Kong（香港大学天体物理研究所）；Department of Physics, University of Hong Kong（香港大学物理系）
The early X-ray afterglows of gamma-ray bursts (GRBs) are usually well described by absorbed power laws. However, in some cases, additional thermal components have been identified. The origin of this emission is debated, with proposed explanations including supernova shock breakout, emission from a cocoon surrounding the jet, as well as emission from the jet itself. A larger sample of detections is needed in order to place constraints on these different models. Here we present a time-resolved spectral analysis of 74 GRBs observed by Swift XRT in a search for thermal components. We report six d…
Study of shock wave dynamics produced by interaction of a fireball with the surrounding medium to it, to explain the x-ray afterglow of Gamma Ray Burst-GRBs
Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent a fantastic opportunity to investigate unique properties not exhibited in other sources. Multi-wavelength afterglow observations from some short- and long-duration GRBs reveal an atypical long-lasting emission that evolves differently from the canonical afterglow light curves favoring the off-axis emission. We present an analytical synchrotron afterglow scenario, and the hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified surrounding environment. The analytical synchrotron afterglow model …
Jet precessions are widely involved in astrophysical phenomena from galaxies to X-ray binaries and gamma-ray bursts (GRBs). Polarization presents a unique probe of the magnetic fields in GRB jets. The precession of GRBs relativistic jets will change the geometry within the observable emitting region of the jet, which can potentially affect the polarization of the afterglow. In this paper, we take into account jet precession to study the polarization evolution and corresponding light curves in GRB early optical afterglows with ordered and random magnetic field geometries. We find that the jet p…
The X-ray afterglow plateau emission observed in many Gamma-ray Bursts (GRBs) has been interpreted as either being fueled by fallback onto a newly formed black hole, or by the spin-down luminosity of an ultra-magnetized millisecond neutron star. If the latter model is assumed, GRB X-ray afterglow light curves can be analytically reproduced. We fit a sample of GRB X-ray plateaus, interestingly yielding a distribution in the magnetic field versus spin period (B-P) diagram consistent with $B\propto P^{7/6}$. This is expected from the well-established physics of the spin-up line minimum period for…
X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from Gamma-ray Bursts
Long gamma-ray bursts (GRBs) are considered to be originated from core collapse of massive stars. It is believed that the afterglow property is determined by the density of the material in the surrounding interstellar medium. Therefore, the circumburst density can be used to distinguish between an interstellar wind $n(R) \propto R^{\rm -k}$, and a constant density medium (ISM), $n(R) = const$. Previous studies with different afterglow samples, show that the circumburst medium of GRBs is neither simply supported by an interstellar wind, nor completely favored by an ISM. In this work, our new sa…
Very long and precise follow-up measurements of the X-ray afterglow of very intense gamma ray bursts (GRBs) allow a critical test of GRB theories. Here we show that the single power-law decay with time of the X-ray afterglow of GRB 130427A, the record long and most accurately measured X-ray afterglow of an intense GRB by the Swift, Chandra and XMM Newton space observatories, and of all other known intense GRBs, is that predicted by the cannonball (CB) model of GRBs from their measured spectral index, while it disagrees with that predicted by the widely accepted fireball (FB) models of GRBs.
The central engine of gamma-ray bursts (GRBs) remains an open and forefront topic in the era of multimessenger astrophysics. The X-ray plateaus appear in some GRB afterglows, which are widely considered to originate from the spindown of magnetars. According to the stable magnetar scenario of GRBs, an X-ray plateau and a decay phase as $\sim t^{-2}$ should appear in X-ray afterglows. Meanwhile, the ``normal'' X-ray afterglow is produced by the external shock from GRB fireball. We analyze the Neil Gehrels \emph{Swift} GRB data, then find three gold samples, which have an X-ray plateau and a deca…
The late-time high-resolution X-ray and radio observations of GRB980425/SN1998bw, the closest known gamma ray burst (GRB) associated with a supernova (SN) explosion, may have actually resolved the hyperluminal source that produced the GRB and its afterglow. Its hyperluminal speed ~350c is consistent with that expected in the cannonball (CB) model of GRBs. The observed superluminal expansion of the late-time radio image of GRB030329/SN2003dh, the GRB with the brightest and longest followed up radio afterglow to date, is also consistent with that expected in the CB model of GRBs and extrapolates…
Flares in the X-ray afterglow of gamma-ray bursts (GRBs) share more characteristics with the prompt emission than the afterglow, such as pulse profile and contained fluence. As a result, they are believed to originate from late-time activity of the central engine and can be used to constrain the overall energy budget. In this paper, we collect a sample of $19$ long GRBs observed by \emph{Swift}-XRT that contain giant flares in their X-ray afterglows. We fit this sample with a version of the magnetar propeller model, modified to include fallback accretion. This model has already successfully re…
Detection of TeV emission during early afterglow from poorly localized GRBs with ground based IACTs
Gran Sasso Science Institute（格兰萨索科学研究所）；INFN - Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所-格兰萨索国家实验室）；INAF - Osseravtorio Astronomico di Roma（意大利国家天体物理研究所-罗马天文台）；INAF - Osservatorio Astronomico d’Abruzzo（意大利国家天体物理研究所-阿布鲁佐天文台）；Max-Planck-Institut für Physik（马克斯·普朗克物理研究所）；Technische Universität München（慕尼黑工业大学）；Institut de Fisica d’Altes Energies (IFAE)（高能物理研究所）；The Barcelona Institute of Science and Technology（巴塞罗那科学技术研究所）
The nature of the shallow decay phase in the X-ray afterglow of the gamma-ray burst (GRB) is not yet clarified. We analyze the data of early X-ray afterglows of 26 GRBs triggered by Burst Alert Telescope onboard Neil Gehrels Swift Observatory and subsequently detected by Fermi Large Area Telescope (LAT) and/or Imaging Atmospheric Cherenkov Telescopes. It is found that 9 events (including 2 out of 3 very-high-energy gamma-ray events) have no shallow decay phase and that their X-ray afterglow light curves are well described by single power-law model except for the jet break at later epoch. The r…
Gamma-ray burst (GRB) afterglow emission can be observed from sub-TeV to radio wavelengths, though only 6.6\% of observed GRBs present radio afterglows. We examine GRB radio light curves (LCs) to look for the presence of radio plateaus, resembling the plateaus observed in X-ray and optical. We analyze 404 GRBs from the literature with observed radio afterglow and fit 82 GRBs with at least 5 data points with a broken power law (BPL) model, requiring 4 parameters. From these, we find 18 GRBs that present a break feature resembling a plateau. We conduct the first multi-wavelength study of the Dai…
In the numerical modeling of the GRB afterglow, some approximations have been made for simplicity, and different groups developed their codes. A robust test of these models/approaches is challenging because of the lack of directly measured physical parameters. Fortunately, the viewing angle inferred from the afterglow modeling is widely anticipated to be the same as the inclination angle of the binary neutron star (BNS) mergers that can be evaluated with the gravitational wave (GW) data. Therefore in the future, it is possible to calibrate the afterglow modeling with the GW inclination angle m…
