The space-based multi-band astronomical Variable Object Monitor(SVOM) mission is dedicated to the detection,localization and broad-band study of gamma-ray bursts(GRBs) and other high-energy transient phenomena.The gam...The space-based multi-band astronomical Variable Object Monitor(SVOM) mission is dedicated to the detection,localization and broad-band study of gamma-ray bursts(GRBs) and other high-energy transient phenomena.The gamma ray monitor(GRM) onboard is designed to observe GRBs up to 5 MeV.With this instrument,one of the key GRB parameters,Epeak,can be easily measured in the hard X-ray band.It can achieve a detection rate of 100 GRBs per year which ensures the scientific output of SVOM.展开更多
伽马射线暴(Gamma Ray Burst,GRB)的分类问题是天文学领域中未解决的热点问题。根据不同方法采用不同指标进行分类,导致的分类结果也不同。为了建立更合理的分类指标,本文以静止系峰值能量E_(p,i) E、各向同性瞬时等值能量E_(iso) 、瞬...伽马射线暴(Gamma Ray Burst,GRB)的分类问题是天文学领域中未解决的热点问题。根据不同方法采用不同指标进行分类,导致的分类结果也不同。为了建立更合理的分类指标,本文以静止系峰值能量E_(p,i) E、各向同性瞬时等值能量E_(iso) 、瞬时辐射持续时间T_(90,i) 作为解释变量,建立了广义线性分类模型,得到了一个新的分类响应指标gEHD。通过在benchmark数据集上的实验表明,gEHD指标和EHD指标具有等效的分类结果,可作为伽马射线暴Ⅰ型/Ⅱ型的一种新的分类依据。展开更多
The equation of motion for a relativistic neutral particle that moves in a medium characterized by a friction proportional to the square of the velocity is analyzed. The relativistic trajectory is derived in a numeric...The equation of motion for a relativistic neutral particle that moves in a medium characterized by a friction proportional to the square of the velocity is analyzed. The relativistic trajectory is derived in a numerical way and in the form of a Taylor series. The astrophysical applications cover the trajectory of SN 1993J and the light curve of gamma ray bursts.展开更多
According to a recent calculation, 10<sup>58</sup> erg of radiant energy was released by Sgr A*, when it formed the Fermi bubbles. Here, it is argued that this explosion constituted a long gamma-ray burst. .
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:electron synchrotron emission ...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:electron synchrotron emission and 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 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 energy E ≥ 1051 ergs and the fraction of electron energy εe≥ 0.1.This provides a possible explanation for the high energy tail of SGRB 081024B.展开更多
POLAR is a compact polarimeter dedicated to measuring the polarization of GRBs between 50-350 keV.The light collection of 200 mm×6 mm×6 mm plastic bars has been simulated and optimized in order to get unifor...POLAR is a compact polarimeter dedicated to measuring the polarization of GRBs between 50-350 keV.The light collection of 200 mm×6 mm×6 mm plastic bars has been simulated and optimized in order to get uniform response to X-rays at different points along one single bar.According to the Monte Carlo results,the amplitude uniformity strongly depends on the level of polishing of the scintillator surface and the covering.A uniformity of 89% is achieved with a prototype constructed by a non position-sensitive PMT and an array of 4×4 bars.展开更多
Linear polarization has been observed in both the prompt phase and afterglow of some bright gamma-ray bursts（GRBs）.Polarization in the prompt phase spans a wide range,and may be as high as 50%.In the afterglow phas...Linear polarization has been observed in both the prompt phase and afterglow of some bright gamma-ray bursts（GRBs）.Polarization in the prompt phase spans a wide range,and may be as high as 50%.In the afterglow phase,however,it is usually below 10%.According to the standard fireball model,GRBs are produced by synchrotron radiation and Compton scattering process in a highly relativistic jet ejected from the central engine.It is widely accepted that prompt emissions occur in the internal shock when shells with different velocities collide with each other,and the magnetic field advected by the jet from the central engine can be ordered on a large scale.On the other hand,afterglows are often assumed to occur in the external shock when the jet collides with interstellar medium,and the magnetic field produced by the shock through,for example,Weibel instability,is possibly random.In this paper,we calculate the polarization properties of the synchrotron self-Compton process from a highly relativistic jet,in which the magnetic field is randomly distributed in the shock plane.We also consider the generalized situation where a uniform magnetic component perpendicular to the shock plane is superposed on the random magnetic component.We show that it is difficult for the polarization to be larger than 10% if the seed electrons are isotropic in the jet frame.This may account for the observed upper limit of polarization in the afterglow phase of GRBs.In addition,if the random and uniform magnetic components decay with time at different speeds,then the polarization angle may change 90° during the temporal evolution.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2009CB824800)
文摘The space-based multi-band astronomical Variable Object Monitor(SVOM) mission is dedicated to the detection,localization and broad-band study of gamma-ray bursts(GRBs) and other high-energy transient phenomena.The gamma ray monitor(GRM) onboard is designed to observe GRBs up to 5 MeV.With this instrument,one of the key GRB parameters,Epeak,can be easily measured in the hard X-ray band.It can achieve a detection rate of 100 GRBs per year which ensures the scientific output of SVOM.
文摘The equation of motion for a relativistic neutral particle that moves in a medium characterized by a friction proportional to the square of the velocity is analyzed. The relativistic trajectory is derived in a numerical way and in the form of a Taylor series. The astrophysical applications cover the trajectory of SN 1993J and the light curve of gamma ray bursts.
文摘According to a recent calculation, 10<sup>58</sup> erg of radiant energy was released by Sgr A*, when it formed the Fermi bubbles. Here, it is argued that this explosion constituted a long gamma-ray burst. .
基金supported by the National Basic Research Program of China (Grant No. 2009CB824800)the Foundation for the Authors of National Excellent Doctoral Dissertations of Chinathe Qing Lan Project and the NCET Grant
文摘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:electron synchrotron emission and 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 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 energy E ≥ 1051 ergs and the fraction of electron energy εe≥ 0.1.This provides a possible explanation for the high energy tail of SGRB 081024B.
基金supported by the National Basic Research Program of China (Grant No. 2009CB824800)
文摘POLAR is a compact polarimeter dedicated to measuring the polarization of GRBs between 50-350 keV.The light collection of 200 mm×6 mm×6 mm plastic bars has been simulated and optimized in order to get uniform response to X-rays at different points along one single bar.According to the Monte Carlo results,the amplitude uniformity strongly depends on the level of polishing of the scintillator surface and the covering.A uniformity of 89% is achieved with a prototype constructed by a non position-sensitive PMT and an array of 4×4 bars.
基金Supported by Fundamental Research Funds for the Central Universities(106112016CDJCR301206)National Natural Science Fund of China(11375203,11603005)Open Project Program of State Key Laboratory of Theoretical Physics,Institute of Theoretical Physics,Chinese Academy of Sciences,China(Y5KF181CJ1)
文摘Linear polarization has been observed in both the prompt phase and afterglow of some bright gamma-ray bursts（GRBs）.Polarization in the prompt phase spans a wide range,and may be as high as 50%.In the afterglow phase,however,it is usually below 10%.According to the standard fireball model,GRBs are produced by synchrotron radiation and Compton scattering process in a highly relativistic jet ejected from the central engine.It is widely accepted that prompt emissions occur in the internal shock when shells with different velocities collide with each other,and the magnetic field advected by the jet from the central engine can be ordered on a large scale.On the other hand,afterglows are often assumed to occur in the external shock when the jet collides with interstellar medium,and the magnetic field produced by the shock through,for example,Weibel instability,is possibly random.In this paper,we calculate the polarization properties of the synchrotron self-Compton process from a highly relativistic jet,in which the magnetic field is randomly distributed in the shock plane.We also consider the generalized situation where a uniform magnetic component perpendicular to the shock plane is superposed on the random magnetic component.We show that it is difficult for the polarization to be larger than 10% if the seed electrons are isotropic in the jet frame.This may account for the observed upper limit of polarization in the afterglow phase of GRBs.In addition,if the random and uniform magnetic components decay with time at different speeds,then the polarization angle may change 90° during the temporal evolution.
