The phenomenon of gamma-ray burst （GRB） spectral lags is very common, but a definitive explanation has not yet been given. From a sample of 82 GRB pulses we find that the spectral lags are correlated with the pulse ...The phenomenon of gamma-ray burst （GRB） spectral lags is very common, but a definitive explanation has not yet been given. From a sample of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths, however, there is no correlation between the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay due to the curvature effect.展开更多
Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are locat...Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.展开更多
Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other pa...Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other parameters for a sample of nine long bursts, using the general cross-correlation technique that includes the lag between two different energy bands. We conclude that the distribution of RSLs is normal and has a mean value of 0.1; that the RSLs are weakly correlated with the FWHM, the asymmetry, peak flux （Fp）, peak energy （Ep） and spectral indexes （α and β）, while they are uncorrelated with τ31, the hardness- ratio （HR31） and the peak time （tm）. Our important discovery is that redshift （z） and peak luminosity （Lp） are strongly correlated with the RSL, which can be measured easily and directly, making the RSL a good redshift and peak luminosity indicator.展开更多
It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star(NS)merger event,GW170817/GRB 170817A/kilonova AT2017gfo,places irreconcilable constraints to models of th...It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star(NS)merger event,GW170817/GRB 170817A/kilonova AT2017gfo,places irreconcilable constraints to models of the prompt emission of this gamma-ray burst(GRB).The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously.We argue that the merger remnant should be an NS(last for,at least,a large fraction of 1 s),and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of effective viscosity in the disk.Further,we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS.If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A,thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable.If our scenario is verified,it would be of interest to investigate the cooling of nascent NSs.展开更多
Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst （GRB） appears to be anti-correlated with the redshift of the burst. In order to confirm th...Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst （GRB） appears to be anti-correlated with the redshift of the burst. In order to confirm this finding, we analyzed 10 GRBs detected by HETE-2 with known redshifts and found a similar relation. Using the relation, we estimated the redshifts of 878 long GRBs in the BATSE catalog, then we investigated the distributions of the redshifts and 869 Eiso of these GRBs. The distribution of the estimated redshifts is concentrated at z = 1.4 and the distribution of Eiso peaks at 10^52.5 erg. The underlying physics of the correlation is unclear at present.展开更多
We analyzed a sample of 66 gamma-ray bursts （GRBs） and statistically confirmed the prediction on the time curve of the hardness ratio of GRBs made by Qin et al. based on the curvature effect. In their analysis, GRB ...We analyzed a sample of 66 gamma-ray bursts （GRBs） and statistically confirmed the prediction on the time curve of the hardness ratio of GRBs made by Qin et al. based on the curvature effect. In their analysis, GRB pulses are divided into three types according to the shape of their raw hardness ratio （RHR） time curves, defined as to include the background counts to the signal counts, so as to make use of counts within small time intervals. Of the three types, very hard sources exhibit a perfect pulse-like profile （type 1）, hard bursts possess a pulse-like profile with a dip in the decay phase （type 2）, and soft bursts show no pulse-like profile but have only a dipped profile （type 3）. In terms of the conventional hardness ratio, type 3 sources are indeed generally softer than those of type 1 and type 2, in agreement with the prediction. We found that the minimum value of RHR is sensitive in distinguishing the different types. We propose that GRB pulses can be classified according to the minimum value of RHR and that the different type sources may be connected with different strengths of the shock or/and the magnetic field.展开更多
Appearing in the composite spectral data of BATSE, EGRET and COMPTEL for GRB 910503, there is a bump at around 1600keV. We perform a statistical analysis on the spectral data, trying to find out if the bump could be a...Appearing in the composite spectral data of BATSE, EGRET and COMPTEL for GRB 910503, there is a bump at around 1600keV. We perform a statistical analysis on the spectral data, trying to find out if the bump could be accounted for by a blue-shifted and significantly broadened rest frame line due to the Doppler effect of an expanding fireball surface. We made an F-test and adopted previously proposed criteria. The study reveals that the criteria are well satisfied and the feature can be interpreted as the blue shifted 6.4 keV line. From the fit with this line taken into account, we find the Lorentz factor of this source to be F = 116-9^＋9 （at the 68% confident level, △X^2 = 1） and the rest frame spectral peak energy to be E0,p=2.96-0.18^＋0.24 ke V.Although the existence of the emission line feature requires other independent tests to confirm, the analysis suggests that it is feasible to detect emission line features in the high energy range of GRB spectra when taking into account the Doppler effect of fireball expansion.展开更多
We investigate the forming of gamma-ray burst pulses with a simple onedimensional relativistic shock model. The mechanism is that a ＂central engine＂ drives forward the nearby plasma inside the fireball to generate a...We investigate the forming of gamma-ray burst pulses with a simple onedimensional relativistic shock model. The mechanism is that a ＂central engine＂ drives forward the nearby plasma inside the fireball to generate a series of pressure waves. We give a relativistic geometric recurrence formula that connects the time when the pressure waves are produced and the time when the corresponding shocks occurred. This relation enables us to relate the pulse magnitude with the observation time. Our analysis shows that the evolution of the pressure waves leads to a fast rise and an exponential decay pulses. In determining the width of the pulses, the acceleration time is more important than that of the deceleration.展开更多
Observations on relativistic jets in radio galaxies, active galactic nuclei, and 'microquasars' revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evoluti...Observations on relativistic jets in radio galaxies, active galactic nuclei, and 'microquasars' revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind.展开更多
GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to~1020 s and the true timescale of the central engine activity t_(burst)≥4×10^(4) s.The late X-ray light cur...GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to~1020 s and the true timescale of the central engine activity t_(burst)≥4×10^(4) s.The late X-ray light curve with a decay index ofα=7.53 is steeper than the steepest possible decay from an external shock model.We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage,while the magnetar collapsed into the black hole before its spindown,resulting in a very steep decay of the late X-ray light curve.The optical data show that the light curve is still rising after 1.1 ks,suggesting a late onset.We show that GRB 200612A’s optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet.This is a special case among GRBs,as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.展开更多
Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the d...Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.展开更多
Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope...Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope （LAT） on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars： log Blc （G） are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average： logE（erg s-1） = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.展开更多
Jet precession has previously been proposed to explain the apparently repeating features in the light curves of a few gamma-ray bursts(GRBs).In this paper,we further apply the precession model to a bright GRB 220408B ...Jet precession has previously been proposed to explain the apparently repeating features in the light curves of a few gamma-ray bursts(GRBs).In this paper,we further apply the precession model to a bright GRB 220408B by examining both its temporal and spectral consistency with the predictions of the model.As one of the recently confirmed GRBs observed by our GRID CubeSat mission,GRB 220408B is noteworthy as it exhibits three apparently similar emission episodes.Furthermore,the similarities are reinforced by their strong temporal correlations and similar features in terms of spectral evolution and spectral lags.Our analysis demonstrates that these features can be well explained by the modulated emission of a Fast-Rise-Exponential-Decay(FRED)shape light curve intrinsically produced by a precessing jet with a precession period of 18.4_(-0.2)~(+0.2)s,a nutation period of11.1_(-0.2)~(+0.2)s and viewed off-axis.This study provides a straightforward explanation for the complex yet similar multiepisode GRB light curves.展开更多
The quasi-simultaneous multi-wavelength emission of TeV blazar 3C 66A is studied by using a one-zone multi-component leptonic jet model. It is found that the quasi-simultaneous spectral energy distribution of 3C 66A c...The quasi-simultaneous multi-wavelength emission of TeV blazar 3C 66A is studied by using a one-zone multi-component leptonic jet model. It is found that the quasi-simultaneous spectral energy distribution of 3C 66A can be well reproduced; in particular, the first three months of its average Fermi-LAT spectrum can be well reproduced by the synchrotron self-Compton component plus external Compton component of the broad line region （BLR）. Clues to its redshift and gamma-ray emission location are obtained. The results indicate the following. （i） On the redshift： The theoretical intrinsic TeV spectra can be predicted by extrapolating the reproduced GeV spectra. Through comparing these extrapolated TeV spectra with the corrected observed TeV spectra from extragalactic background light, it is suggested that the redshift of 3C 66A could be between 0.1 and 0.3, with the most likely value being ~ 0.2. （ii） On the gamma-ray emission location： To well reproduce the GeV emission of 3C 66A under different assumptions on the BLR, the gamma-ray emission region is always required to be beyond the inner zone of the BLR. The BLR absorption effect on gamma-ray emission confirms this point.展开更多
The growing observed evidence shows that the long-and short-duration gamma-ray bursts(GRBs) originate from massive star core-collapse and the merger of compact stars,respectively.GRB 201221 D is a short-duration GRB l...The growing observed evidence shows that the long-and short-duration gamma-ray bursts(GRBs) originate from massive star core-collapse and the merger of compact stars,respectively.GRB 201221 D is a short-duration GRB lasting~0.1 s without extended emission at high redshift z=1.046.By analyzing data observed with the Swift/BAT and Fermi/GBM,we find that a cutoff power-law model can adequately fit the spectrum with a soft E=113keV,and isotropic energy E=1.36× 10erg.In order to reveal the possible physical origin of GRB 201221 D,we adopted multi-wavelength criteria(e.g.,Amati relation,ε-parameter,amplitude parameter,local event rate density,luminosity function,and properties of the host galaxy),and find that most of the observations of GRB 201221 D favor a compact star merger origin.Moreover,we find that α is larger than 2+βin the prompt emission phase which suggests that the emission region is possibly undergoing acceleration during the prompt emission phase with a Poynting-flux-dominated jet.展开更多
The afterglow of GRB 081029 showed unusual behavior, with a signifi- cant rebrightening being observed at the optical wavelength at about 3000 s after the burst. One possible explanation is that the rebrightening resu...The afterglow of GRB 081029 showed unusual behavior, with a signifi- cant rebrightening being observed at the optical wavelength at about 3000 s after the burst. One possible explanation is that the rebrightening resulted from an energy in- jection. Here we present a detailed numerical study of the energy injection process and interpret the X-ray and optical afterglow light curves of GRB 081029. In our model, we have assumed two periods of energy injection, each with a constant injec- tion power. One injection starts at 2.8 × 10^3 s and lasts for about 2500 s, with a power of 7.0 × 10^47 erg s-1. This energy injection mainly accounts for the rapid rebrighten- ing at about 3000 s. The other injection starts at 8.0 × 10^3 s and lasts for about 5000 s. The injection power is 3.5 × 10^47 erg s-1. This energy injection can help to explain the slight rebrightening at about 10 000 s. It is shown that the observed optical after- glow, especially the marked rebrightening at about 3000 s, can be reproduced well. In the X-ray band, the predicted amplitude of the rebrightening is much shallower, which is also consistent with the observed X-ray afterglow light curve. It is argued that the two periods of energy injection can be produced by clumpy materials falling onto the central compact object of the burster, which leads to an enhancement of accretion and gives rise to a strong temporary outflow.展开更多
High energy emission （〉 tens MeV） of Gamma-Ray Bursts （GRBs） provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has...High energy emission （〉 tens MeV） of Gamma-Ray Bursts （GRBs） provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has been well identified in about half of Swift Gamma-ray Burst x-ray afterglows. The widely considered interpretation inv.olves a significant energy injection and possibly time-evolving shock parameter（s）. We calculate the synchrotron-self-Compton （SSC） radiation of such an external forward shock and show that it could explain the well-known long term high energy （i.e., tens MeV to GeV） afterglow of GRB 940217. We propose that cooperation of Swift and GLAST will help to reveal the nature of GRBs.展开更多
Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting~1 s.The light curve of the pr...Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting~1 s.The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with E_p=1826±747.More interestingly,it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of~10^(4)s,and then follows a rapid decay with a decay slope~3.2.This temporal feature is challenging by invoking the external shock mode.In this paper,we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar,and the abrupt decay following the longlasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole.It is the short GRB(SGRB)with the longest X-ray internal plateau emission powered by a supra-massive neutron star.If this is the case,one can estimate the physical parameters of a supra-massive magnetar,and compare with other SGRBs.We also discuss the possible gravitational-wave emission,which is powered by a supra-massive magnetar and its detectability,and the possible kilonova emission,which is powered by r-process and magnetar spin-down to compare with the observed data.展开更多
The X-ray flares have usually been ascribed to long-lasting activities of the central engine of gamma-ray bursts(GRBs),e.g.,fallback accretion.The GRB X-ray plateaus,however,favor a millisecond magnetar central engine...The X-ray flares have usually been ascribed to long-lasting activities of the central engine of gamma-ray bursts(GRBs),e.g.,fallback accretion.The GRB X-ray plateaus,however,favor a millisecond magnetar central engine.The fallback accretion can be significantly suppressed due to the propeller effect of a magnetar.Therefore,if the propeller regime cannot resist the mass flow onto the surface of the magnetar efficiently,the X-ray flares raising upon the magnetar plateau would be expected.In this work,such peculiar cases are connected to the accretion process of the magnetars,and an implication for magnetar-disc structure is given.We investigate the repeated accretion process with multi-flare GRB 050730,and give a discussion for the accretion-induced variation of the magnetic field in GRB 111209 A.Two or more flares exhibit in the GRB 050730,060607 A and 140304 A;by adopting magnetar mass M=1.4 M_(⊙)and radius R=12 km,the average mass flow rates of the corresponding surrounding disk are 3.53×10^(-4)M_(⊙)s^(-1).4.23×10^(-4)M_(⊙)s^(-1),and 4.33×10^(-4)M_(⊙)s^(-1),and the corresponding average sizes of the magnetosphere are 5.01×10^(6)cm,6.45 x 10^(-6)cm,and 1.09×10^(-7)cm,respectively.A statistic analysis that contains eight GRBs within 12 flares shows that the total mass loading in single flare is~2×10^(-5)M_(⊙).In the lost mass of a disk,there are about 0.1%used to feed a collimated jet.展开更多
Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts（GRBs） and electromagnetic（EM） counterparts of gravitational waves（GWs）. Based on n...Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts（GRBs） and electromagnetic（EM） counterparts of gravitational waves（GWs）. Based on near real-time Fermi/GBM data, we developed a low-latency pipeline to automatically calculate the temporal and spectral properties of GRBs. With this pipeline, some important parameters can be obtained, such as T_（90） and fluence, within ～ 20 min after the GRB trigger.For ～ 90% of GRBs, T90 and fluence are consistent with the GBM catalog results within 2σ errors.This pipeline has been used by the Gamma-ray Bursts Polarimeter（POLAR） and the Insight Hard Xray Modulation Telescope（Insight-HXMT） to follow up the bursts of interest. For GRB 170817 A, the first EM counterpart of GW events detected by Fermi/GBM and INTEGRAL/SPI-ACS, the pipeline gave T90 and spectral information 21 min after the GBM trigger, providing important information for POLAR and Insight-HXMT observations.展开更多
基金the National Natural Science Foundation of China.
文摘The phenomenon of gamma-ray burst （GRB） spectral lags is very common, but a definitive explanation has not yet been given. From a sample of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths, however, there is no correlation between the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay due to the curvature effect.
基金a RGC grant of the Hong Kong Government and the National Natural Science Foundation of China.
文摘Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.
基金Supported by the National Natural Science Foundation of China.
文摘Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other parameters for a sample of nine long bursts, using the general cross-correlation technique that includes the lag between two different energy bands. We conclude that the distribution of RSLs is normal and has a mean value of 0.1; that the RSLs are weakly correlated with the FWHM, the asymmetry, peak flux （Fp）, peak energy （Ep） and spectral indexes （α and β）, while they are uncorrelated with τ31, the hardness- ratio （HR31） and the peak time （tm）. Our important discovery is that redshift （z） and peak luminosity （Lp） are strongly correlated with the RSL, which can be measured easily and directly, making the RSL a good redshift and peak luminosity indicator.
基金the National SKA Program of China(2020SKA0120100)research projects of Henan Science and Technology Committee(212300410378)the National NaturalScience Foundationof China(NSFC)grant(U1938116).
文摘It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star(NS)merger event,GW170817/GRB 170817A/kilonova AT2017gfo,places irreconcilable constraints to models of the prompt emission of this gamma-ray burst(GRB).The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously.We argue that the merger remnant should be an NS(last for,at least,a large fraction of 1 s),and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of effective viscosity in the disk.Further,we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS.If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A,thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable.If our scenario is verified,it would be of interest to investigate the cooling of nascent NSs.
基金Supported by the National Natural Science Foundation of China.
文摘Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst （GRB） appears to be anti-correlated with the redshift of the burst. In order to confirm this finding, we analyzed 10 GRBs detected by HETE-2 with known redshifts and found a similar relation. Using the relation, we estimated the redshifts of 878 long GRBs in the BATSE catalog, then we investigated the distributions of the redshifts and 869 Eiso of these GRBs. The distribution of the estimated redshifts is concentrated at z = 1.4 and the distribution of Eiso peaks at 10^52.5 erg. The underlying physics of the correlation is unclear at present.
基金the National Natural Science Foundation of China(Grants 10533050 and 10573030)
文摘We analyzed a sample of 66 gamma-ray bursts （GRBs） and statistically confirmed the prediction on the time curve of the hardness ratio of GRBs made by Qin et al. based on the curvature effect. In their analysis, GRB pulses are divided into three types according to the shape of their raw hardness ratio （RHR） time curves, defined as to include the background counts to the signal counts, so as to make use of counts within small time intervals. Of the three types, very hard sources exhibit a perfect pulse-like profile （type 1）, hard bursts possess a pulse-like profile with a dip in the decay phase （type 2）, and soft bursts show no pulse-like profile but have only a dipped profile （type 3）. In terms of the conventional hardness ratio, type 3 sources are indeed generally softer than those of type 1 and type 2, in agreement with the prediction. We found that the minimum value of RHR is sensitive in distinguishing the different types. We propose that GRB pulses can be classified according to the minimum value of RHR and that the different type sources may be connected with different strengths of the shock or/and the magnetic field.
基金Supported by the National Natural Science Foundation of China.
文摘Appearing in the composite spectral data of BATSE, EGRET and COMPTEL for GRB 910503, there is a bump at around 1600keV. We perform a statistical analysis on the spectral data, trying to find out if the bump could be accounted for by a blue-shifted and significantly broadened rest frame line due to the Doppler effect of an expanding fireball surface. We made an F-test and adopted previously proposed criteria. The study reveals that the criteria are well satisfied and the feature can be interpreted as the blue shifted 6.4 keV line. From the fit with this line taken into account, we find the Lorentz factor of this source to be F = 116-9^＋9 （at the 68% confident level, △X^2 = 1） and the rest frame spectral peak energy to be E0,p=2.96-0.18^＋0.24 ke V.Although the existence of the emission line feature requires other independent tests to confirm, the analysis suggests that it is feasible to detect emission line features in the high energy range of GRB spectra when taking into account the Doppler effect of fireball expansion.
基金Supported by the National Natural Science Foundation of China.
文摘We investigate the forming of gamma-ray burst pulses with a simple onedimensional relativistic shock model. The mechanism is that a ＂central engine＂ drives forward the nearby plasma inside the fireball to generate a series of pressure waves. We give a relativistic geometric recurrence formula that connects the time when the pressure waves are produced and the time when the corresponding shocks occurred. This relation enables us to relate the pulse magnitude with the observation time. Our analysis shows that the evolution of the pressure waves leads to a fast rise and an exponential decay pulses. In determining the width of the pulses, the acceleration time is more important than that of the deceleration.
基金Supported by the National Natural Science Foundation of China.
文摘Observations on relativistic jets in radio galaxies, active galactic nuclei, and 'microquasars' revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind.
基金supported by the National Natural Science Foundation of China(Nos.U1938201 and 12373042)。
文摘GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to~1020 s and the true timescale of the central engine activity t_(burst)≥4×10^(4) s.The late X-ray light curve with a decay index ofα=7.53 is steeper than the steepest possible decay from an external shock model.We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage,while the magnetar collapsed into the black hole before its spindown,resulting in a very steep decay of the late X-ray light curve.The optical data show that the light curve is still rising after 1.1 ks,suggesting a late onset.We show that GRB 200612A’s optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet.This is a special case among GRBs,as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.
基金Supported by the National Natural Science Foundation of China
文摘Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.
基金financial support of Basic Research Program of the Presidium of the Russian Academy of Sciences"Transitional and Explosive Processes in Astrophysics(P-41)"Russian Foundation for Basic Research(grant 16–02–00954)
文摘Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope （LAT） on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars： log Blc （G） are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average： logE（erg s-1） = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.
基金support by the National Key Research and Development Programs of China(2022YFF0711404,2022SKA0130102)the National SKA Program of China(2022SKA0130100)+4 种基金the National Natural Science Foundation of China(grant Nos.11833003,U2038105,U1831135,12121003)the science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B11the Fundamental Research Funds for the Central Universitiesthe Program for Innovative Talents and Entrepreneur in Jiangsusupported by the National Postdoctoral Program for Innovative Talents(grant No.BX20200164)。
文摘Jet precession has previously been proposed to explain the apparently repeating features in the light curves of a few gamma-ray bursts(GRBs).In this paper,we further apply the precession model to a bright GRB 220408B by examining both its temporal and spectral consistency with the predictions of the model.As one of the recently confirmed GRBs observed by our GRID CubeSat mission,GRB 220408B is noteworthy as it exhibits three apparently similar emission episodes.Furthermore,the similarities are reinforced by their strong temporal correlations and similar features in terms of spectral evolution and spectral lags.Our analysis demonstrates that these features can be well explained by the modulated emission of a Fast-Rise-Exponential-Decay(FRED)shape light curve intrinsically produced by a precessing jet with a precession period of 18.4_(-0.2)~(+0.2)s,a nutation period of11.1_(-0.2)~(+0.2)s and viewed off-axis.This study provides a straightforward explanation for the complex yet similar multiepisode GRB light curves.
基金supported by the National Science Foundation of China (Grant Nos. 11063003 and 10963004)the Yunnan Provincial Science Foundation (grant 2009CI040)
文摘The quasi-simultaneous multi-wavelength emission of TeV blazar 3C 66A is studied by using a one-zone multi-component leptonic jet model. It is found that the quasi-simultaneous spectral energy distribution of 3C 66A can be well reproduced; in particular, the first three months of its average Fermi-LAT spectrum can be well reproduced by the synchrotron self-Compton component plus external Compton component of the broad line region （BLR）. Clues to its redshift and gamma-ray emission location are obtained. The results indicate the following. （i） On the redshift： The theoretical intrinsic TeV spectra can be predicted by extrapolating the reproduced GeV spectra. Through comparing these extrapolated TeV spectra with the corrected observed TeV spectra from extragalactic background light, it is suggested that the redshift of 3C 66A could be between 0.1 and 0.3, with the most likely value being ~ 0.2. （ii） On the gamma-ray emission location： To well reproduce the GeV emission of 3C 66A under different assumptions on the BLR, the gamma-ray emission region is always required to be beyond the inner zone of the BLR. The BLR absorption effect on gamma-ray emission confirms this point.
基金supported by the National Natural Science Foundation of China (grant Nos. 11922301 and 12133003)the Guangxi Science Foundation (grant Nos. 2017GXNSFFA198008 and AD17129006)+6 种基金support by the Program of Bagui Young Scholars Program, and special funding for Guangxi distinguished professors (Bagui Yingcai & Bagui Xuezhe)support by the National Key Research and Development Programs of China (2018YFA0404204)the National Natural Science Foundation of China (grant Nos. 11833003 and U2038105)the Program for Innovative Talents, Entrepreneur in Jiangsusupport by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant Nos. XDA15310300, XDA15052100 and XDB23040000)support by the National Natural Science Foundation of China (grant Nos. 12041306 and 12103089)the Natural Science Foundation of Jiangsu Province (grant No. BK20211000)。
文摘The growing observed evidence shows that the long-and short-duration gamma-ray bursts(GRBs) originate from massive star core-collapse and the merger of compact stars,respectively.GRB 201221 D is a short-duration GRB lasting~0.1 s without extended emission at high redshift z=1.046.By analyzing data observed with the Swift/BAT and Fermi/GBM,we find that a cutoff power-law model can adequately fit the spectrum with a soft E=113keV,and isotropic energy E=1.36× 10erg.In order to reveal the possible physical origin of GRB 201221 D,we adopted multi-wavelength criteria(e.g.,Amati relation,ε-parameter,amplitude parameter,local event rate density,luminosity function,and properties of the host galaxy),and find that most of the observations of GRB 201221 D favor a compact star merger origin.Moreover,we find that α is larger than 2+βin the prompt emission phase which suggests that the emission region is possibly undergoing acceleration during the prompt emission phase with a Poynting-flux-dominated jet.
基金supported by the National Natural Science Foundation of China(Grant Nos. 11033002 and J1210039)the National Basic Research Program of China (973 Program, Grant No. 2009CB824800)
文摘The afterglow of GRB 081029 showed unusual behavior, with a signifi- cant rebrightening being observed at the optical wavelength at about 3000 s after the burst. One possible explanation is that the rebrightening resulted from an energy in- jection. Here we present a detailed numerical study of the energy injection process and interpret the X-ray and optical afterglow light curves of GRB 081029. In our model, we have assumed two periods of energy injection, each with a constant injec- tion power. One injection starts at 2.8 × 10^3 s and lasts for about 2500 s, with a power of 7.0 × 10^47 erg s-1. This energy injection mainly accounts for the rapid rebrighten- ing at about 3000 s. The other injection starts at 8.0 × 10^3 s and lasts for about 5000 s. The injection power is 3.5 × 10^47 erg s-1. This energy injection can help to explain the slight rebrightening at about 10 000 s. It is shown that the observed optical after- glow, especially the marked rebrightening at about 3000 s, can be reproduced well. In the X-ray band, the predicted amplitude of the rebrightening is much shallower, which is also consistent with the observed X-ray afterglow light curve. It is argued that the two periods of energy injection can be produced by clumpy materials falling onto the central compact object of the burster, which leads to an enhancement of accretion and gives rise to a strong temporary outflow.
基金the National Natural Science Foundation of China.
文摘High energy emission （〉 tens MeV） of Gamma-Ray Bursts （GRBs） provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has been well identified in about half of Swift Gamma-ray Burst x-ray afterglows. The widely considered interpretation inv.olves a significant energy injection and possibly time-evolving shock parameter（s）. We calculate the synchrotron-self-Compton （SSC） radiation of such an external forward shock and show that it could explain the well-known long term high energy （i.e., tens MeV to GeV） afterglow of GRB 940217. We propose that cooperation of Swift and GLAST will help to reveal the nature of GRBs.
基金supported by the Guangxi Science Foundation(grant No.2023GXNSFDA026007)the Program of Bagui Scholars Program(LHJ)。
文摘Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting~1 s.The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with E_p=1826±747.More interestingly,it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of~10^(4)s,and then follows a rapid decay with a decay slope~3.2.This temporal feature is challenging by invoking the external shock mode.In this paper,we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar,and the abrupt decay following the longlasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole.It is the short GRB(SGRB)with the longest X-ray internal plateau emission powered by a supra-massive neutron star.If this is the case,one can estimate the physical parameters of a supra-massive magnetar,and compare with other SGRBs.We also discuss the possible gravitational-wave emission,which is powered by a supra-massive magnetar and its detectability,and the possible kilonova emission,which is powered by r-process and magnetar spin-down to compare with the observed data.
基金supported by the National Natural Science Foundation of China(Grant No.U1938201)the Guangxi Science Foundation the One-Hundred-Talents Program of Guangxi colleges,the Guangxi Science Foundation(Grant No.2017GXNSFFA198008)Innovation Project of Guangxi Graduate Education(Grant No.YCBZ2020025)。
文摘The X-ray flares have usually been ascribed to long-lasting activities of the central engine of gamma-ray bursts(GRBs),e.g.,fallback accretion.The GRB X-ray plateaus,however,favor a millisecond magnetar central engine.The fallback accretion can be significantly suppressed due to the propeller effect of a magnetar.Therefore,if the propeller regime cannot resist the mass flow onto the surface of the magnetar efficiently,the X-ray flares raising upon the magnetar plateau would be expected.In this work,such peculiar cases are connected to the accretion process of the magnetars,and an implication for magnetar-disc structure is given.We investigate the repeated accretion process with multi-flare GRB 050730,and give a discussion for the accretion-induced variation of the magnetic field in GRB 111209 A.Two or more flares exhibit in the GRB 050730,060607 A and 140304 A;by adopting magnetar mass M=1.4 M_(⊙)and radius R=12 km,the average mass flow rates of the corresponding surrounding disk are 3.53×10^(-4)M_(⊙)s^(-1).4.23×10^(-4)M_(⊙)s^(-1),and 4.33×10^(-4)M_(⊙)s^(-1),and the corresponding average sizes of the magnetosphere are 5.01×10^(6)cm,6.45 x 10^(-6)cm,and 1.09×10^(-7)cm,respectively.A statistic analysis that contains eight GRBs within 12 flares shows that the total mass loading in single flare is~2×10^(-5)M_(⊙).In the lost mass of a disk,there are about 0.1%used to feed a collimated jet.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23040400)the National Natural Science Foundation of China(Grant Nos.11403026,11503028and 11673023)+4 种基金the National Basic Research Program of China(973 program,Grant No.2014CB845800)the National Thousand Young Talents program of Chinafunded by China National Space Administration(CNSA)the Chinese Academy of Sciences(CAS)the University of Geneva(UNIGE)
文摘Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts（GRBs） and electromagnetic（EM） counterparts of gravitational waves（GWs）. Based on near real-time Fermi/GBM data, we developed a low-latency pipeline to automatically calculate the temporal and spectral properties of GRBs. With this pipeline, some important parameters can be obtained, such as T_（90） and fluence, within ～ 20 min after the GRB trigger.For ～ 90% of GRBs, T90 and fluence are consistent with the GBM catalog results within 2σ errors.This pipeline has been used by the Gamma-ray Bursts Polarimeter（POLAR） and the Insight Hard Xray Modulation Telescope（Insight-HXMT） to follow up the bursts of interest. For GRB 170817 A, the first EM counterpart of GW events detected by Fermi/GBM and INTEGRAL/SPI-ACS, the pipeline gave T90 and spectral information 21 min after the GBM trigger, providing important information for POLAR and Insight-HXMT observations.
