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
Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the recently derived 42 gamma-ray bursts(GRBs) data calibrated with the method that can avoid the circularity...Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the recently derived 42 gamma-ray bursts(GRBs) data calibrated with the method that can avoid the circularity problem.The results show that GRBs can be an optional observation to constrain the Cardassian models.Combining the GRBs data with the newly de-rived size of baryonic acoustic oscillation peak from the Sloan Digital Sky Survey(SDSS),and the position of the first acoustic peak of the Cosmic Microwave Background radiation(CMB) from Wilkinson Microwave Anisotropy Probe(WMAP),we find Ωm0=0.27+0.02-0.02,n=0.06+0.07-0.08(1σ) for the original Cardassian model,and Ωm0=0.27+0.23-0.02,n=-0.09+0.23-1.91,β=0.82+2.10-0.62(1σ) for the modified polytropic Cardassian model.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
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.
文摘Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the recently derived 42 gamma-ray bursts(GRBs) data calibrated with the method that can avoid the circularity problem.The results show that GRBs can be an optional observation to constrain the Cardassian models.Combining the GRBs data with the newly de-rived size of baryonic acoustic oscillation peak from the Sloan Digital Sky Survey(SDSS),and the position of the first acoustic peak of the Cosmic Microwave Background radiation(CMB) from Wilkinson Microwave Anisotropy Probe(WMAP),we find Ωm0=0.27+0.02-0.02,n=0.06+0.07-0.08(1σ) for the original Cardassian model,and Ωm0=0.27+0.23-0.02,n=-0.09+0.23-1.91,β=0.82+2.10-0.62(1σ) for the modified polytropic Cardassian model.
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.
