Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate...Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.展开更多
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM),consisting of two microsatellites,is designed to detect gamma-ray bursts associated with gravitational-wave events.Here,we introduce th...Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM),consisting of two microsatellites,is designed to detect gamma-ray bursts associated with gravitational-wave events.Here,we introduce the real-time burst alert system of GECAM,with the adoption of the BeiDou-3 short message communication service.We present the post-trigger operations,the detailed ground-based analysis,and the performance of the system.In the first year of the in-flight operation,GECAM was triggered by 42 gamma-ray bursts.The GECAM real-time burst alert system has the ability to distribute the alert within~1 minute after being triggered,which enables timely follow-up observations.展开更多
Strangeon stars,which are proposed to describe the nature of pulsar-like compact stars,have passed various observational tests.The maximum mass of a non-rotating strangeon star could be high,which implies that the rem...Strangeon stars,which are proposed to describe the nature of pulsar-like compact stars,have passed various observational tests.The maximum mass of a non-rotating strangeon star could be high,which implies that the remnants of binary strangeon star mergers could even be long-lived massive strangeon stars.We study rigidly rotating strangeon stars in the slowly rotating approximation,using the Lennard-Jones model for the equation of state.Rotation can significantly increase the maximum mass of strangeon stars with unchanged baryon numbers,enlarging the mass-range of long-lived strangeon stars.During spin-down after merger,the decrease of radius of the remnant will lead to the release of gravitational energy.Taking into account the efficiency of converting the gravitational energy luminosity to the observed X-ray luminosity,we find that the gravitational energy could provide an alternative energy source for the plateau emission of X-ray afterglow.The fitting results of X-ray plateau emission of some short gamma-ray bursts suggest that the magnetic dipole field strength of the remnants can be much smaller than that of expected when the plateau emission is powered only by spin-down luminosity of magnetars.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
In this paper,we upgrade the constraints for the Earth-mass primordial black hole mergers model based on the first Canadian Hydrogen Intensity Mapping Experiment(CHIME)/fast radio burst(FRB)catalog.Assuming the null h...In this paper,we upgrade the constraints for the Earth-mass primordial black hole mergers model based on the first Canadian Hydrogen Intensity Mapping Experiment(CHIME)/fast radio burst(FRB)catalog.Assuming the null hypothesis that the observed non-repeating FRBs originate from Earth-mass primordial black hole mergers,we find that how the charges were distributed in the primordial black hole population is well described by a double powerlaw function with typical charge value of law function with typical charge value of q_(c)/10^(-5)=1.60_(-0.28)^(+0.28),where the power-law index α_(1)=2.33_(-0.18)^(+0.15) for q<q_(c) and α_(2)=4.56_(-0.26)^(+0.30)for q≥q_(c).Here,q represents the charge of the black hole in units of√GM,where M is the mass of the black hole.Furthermore,we infer the local event rate of the bursts is 8.8_(-2.1)^(+5.7)×10^(4)Gpc^(-3) yr^(-1),which indicates that an abundance of the primordial black hole population f■10^(-4) is needed to account for the observed FRBs by CHIME.The results of this paper lay the basis for further research on the electromagnetic radiation background generated by the merger of primordial black hole mergers.展开更多
Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations.Localization based on the relative counts of different detectors has b...Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations.Localization based on the relative counts of different detectors has been widely used for all-sky gamma-ray monitors.There are two major methods for this count distribution localization:χ^(2)minimization method and the Bayesian method.Here we propose a modified Bayesian method that could take advantage of both the accuracy of the Bayesian method and the simplicity of the χ^(2)method.With comprehensive simulations,we find that our Bayesian method with Poisson likelihood is generally more applicable for various bursts than the χ^(2)method,especially for weak bursts.We further proposed a location-spectrum iteration approach based on the Bayesian inference,which could alleviate the problems caused by the spectral difference between the burst and location templates.Our method is very suitable for scenarios with limited computation resources or timesensitive applications,such as in-flight localization software,and low-latency localization for rapidly follow-up observations.展开更多
The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM)mission is designed to monitor the Gamma-Ray Bursts(GRBs)associated with gravitational waves and other high-energy transient sources...The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM)mission is designed to monitor the Gamma-Ray Bursts(GRBs)associated with gravitational waves and other high-energy transient sources.The mission consists of two microsatellites which are planned to operate at the opposite sides of the Earth.Each GECAM satellite could detect and localize GRBs in about 8 keV-5 MeV with its 25 Gamma-Ray Detectors(GRDs).In this work,we report the in-flight energy calibration of GRDs using the characteristic gamma-ray lines in the background spectra,and show their performance evolution during the commissioning phase.Besides,a preliminary cross-calibration of energy response with Fermi GBM data is also presented,validating the energy response of GRDs.展开更多
Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154sugg...Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154suggests that at least some FRBs can be generated by magnetars.However,the majority of X-ray bursts from magnetars are not associated with radio emission.The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs.Here we report long time spin evolution of SGR J1935+2154 until the end of 2022.According to v and v,the spin evolution of SGR J1935+2154 could be divided into two stages.The first stage evolves relatively steady evolution until 2020 April 27.After the burst activity in2020,the spin of SGR J1935+2154 shows strong variations,especially for v.After the burst activity in 2022October,a new spin-down glitch with△v/v=(-7.2±0.6)×10^(-6)is detected around MJD 59876,which is the second event in SGR J1935+2154.At the end,spin frequency and pulse profile do not show variations around the time of FRB 200428 and radio bursts 221014 and 221021,which supply strong clues to constrain the trigger mechanism of FRBs or radio bursts.展开更多
By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma...By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.In our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding medium.Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but phenomenological.FRB-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel instability.Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently.The resulting emission frequency,luminosity and duration in our model are consistent with FRB data.We find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB(SGRB) with fits to BAT/XRT light curves.展开更多
The well-known correlation between radio luminosity （LR） and X-ray luminosity （Lx）, LR/LX 10^-5, holds for a variety of objects, such as active galactic nuclei, Galactic black holes, solar flares and cool stars....The well-known correlation between radio luminosity （LR） and X-ray luminosity （Lx）, LR/LX 10^-5, holds for a variety of objects, such as active galactic nuclei, Galactic black holes, solar flares and cool stars. Here we extend the relation to gamma-ray bursts （GRBs） and find that the GRBs also obey a similar LR - LX relation, with a slightly different slope of LR ∝ LX^1.1. This relation implies that the explosions that occur on different scales may have a common underlying origin.展开更多
High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars...High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s)follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ0)of GRBs.It is shown that the AGN sample does not agree with the Lp-Ep,z-Γ0 relation of GRBs.In addition,we obtain a tight relation of Lsyn∝Е0.45±0.15δ3.50±0.25 syn,p for FSRQs and NLS1 galaxies,where Lsyn is the luminosity at peak photon energy Esyn,p of the synchrotron radiations.This relation is different from the Lp-Ep,z-Γ0 relation of GRB s.The dependence of Lsyn toδis consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue thatΓ0 may be a representative of the kinetic power of the radiating region and the tight Lp-Ep,z-Γ0 relation is shaped by the radiation physics and the jet power together.展开更多
The relativistic external shock model of gamma-ray burst （GRB） afterglows has been estab- lished with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ee and for the...The relativistic external shock model of gamma-ray burst （GRB） afterglows has been estab- lished with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ee and for the magnetic field eB, the number density of the environment n and the index of the power- law distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as： the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. In this paper, by as- suming all four parameters （except p） change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.展开更多
The Swift/XRT detected the X-ray afterglow of long burst GRB 220117A,which began to rebrighten 300 s after triggering and followed a single power-law decay segment after thousands of seconds of the orbital observation...The Swift/XRT detected the X-ray afterglow of long burst GRB 220117A,which began to rebrighten 300 s after triggering and followed a single power-law decay segment after thousands of seconds of the orbital observation gap.This segment is different from the shallow decay segment(plateau)and flare,and may belong to a giant X-ray bump.We investigated this segment by the fall-back accretion model and found that the model can interpret this segment with reasonable parameter values.Within this physical model scenario,the fall-back accretion rate reaches a peak value~1.70×10~(-5)M_⊙s~(-1)around 300 s in the central engine frame,which is compatible with the late mass supply rate of some low-metallicity massive progenitor stars.The initial black hole(BH)spin is a_0=0.64_(-0.26)~(+0.24)and implies that this re-brightening signature requires a larger BH spin.The total accretion mass during the fall-back process is M_(acc)=(3.09±0.02)×10~(-2)M_⊙.The jet energy from the fall-back accretion is(9.77±0.65)×10~(52)erg,with a ratio of 0.066 to the isotropic-equivalent radiation energies of the GRB prompt phase in the 1-10~4 keV band.The fall-back radius r_p corresponding to the peak time of fall-back t_p is(3.16±0.05)×10~(10)cm,which is consistent with the typical radius of Wolf-Rayet stars.In summary,our results provide additional support for the origin of the long burst from the core collapse of Wolf-Rayet stars,and its late central engine activity is likely due to the fall-back accretion process.展开更多
The physical mechanism of fast radio bursts(FRBs) is still unknown. On 2020 April 28, a special radio burst, FRB200428, was detected and believed to be associated with the Galactic magnetar SGR 1935+2154. It confirms ...The physical mechanism of fast radio bursts(FRBs) is still unknown. On 2020 April 28, a special radio burst, FRB200428, was detected and believed to be associated with the Galactic magnetar SGR 1935+2154. It confirms that at least some of the FRBs were generated by magnetars, although the radiation mechanism continues to be debated.To this end, we study in detail the multiband afterglows of FRB 200428 described by the synchrotron fireball shock model. We find the prediction for the optical and radio afterglows of FRB 200428 is consistent with the observations when considering the post-FRB optical and radio upper limits from the literature. We also show that the follow up detection of the afterglows from fast radio bursts like—FRB 200428 is possible at the radio band,though challenging. Based on our model, one can obtain information about the energy of the fireball, the radiation zone, and the nature of the surrounding medium. That may shed light on the physical mechanism of FRBs.展开更多
In spite of the importance of studying the cosmic generation of heavy elements through the r-process,the detection of a kilonova resulting from the merger of a neutron star binary is still a challenging task.In this p...In spite of the importance of studying the cosmic generation of heavy elements through the r-process,the detection of a kilonova resulting from the merger of a neutron star binary is still a challenging task.In this paper,we show that the Visible Telescope(VT)onboard the ongoing SVOM space mission is powerful for identifying kilonova candidates associated with short gamma-ray bursts up to a distance of 600 Mpc.A significant color variation,turning blue and then turning red,is revealed by calculating the light curves in both red and blue channels of VT by a linear combination of an afterglow and an associated kilonova.The maximum color variation is as high as~0.5-1 mag,which is far larger than the small photometry error of~0.2 mag of VT for a point source with a brightness of 23 mag.Up to a distance of 600 Mpc,~1-2 kilonova candidates per year are predicted to be identified by VT.展开更多
A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral...A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.展开更多
The second(O2)observational campaign of gravitational waves(GWs)organized by the LIGO/Virgo Collaborations has led to several breakthroughs such as the detection of GW signals from merger systems involving black holes...The second(O2)observational campaign of gravitational waves(GWs)organized by the LIGO/Virgo Collaborations has led to several breakthroughs such as the detection of GW signals from merger systems involving black holes or neutrons stars.During O2,14 GW alerts were sent to the astronomical community with sky regions mostly covering over hundreds of square degrees.Among them,six were finally confirmed as real astrophysical events.Since 2013,a new set of ground-based robotic telescopes called Ground-based Wide Angle Camera system(GWAC)project and its pathfinder mini-GWAC has been developed to contribute to the various challenges of multi-messenger and time domain astronomy.The GWAC system is built up in the framework of the ground-segment system of the SVOM mission that will be devoted to the study of the multi-wavelength transient sky in the next decade.During O2,only the mini-GWAC telescope network was fully operational.Due to the wide field of view and fast automatic follow-up capabilities of the mini-GWAC telescopes,they were adept to efficiently cover the sky localization areas of GW event candidates.In this paper,we present the mini-GWAC pipeline we have set up to respond to GW alerts and we report our optical follow-up observations of eight GW alerts detected during the O2 run.Our observations provided the largest coverage of the GW localization areas with a short latency made by any optical facility.We found tens of optical transient candidates in our images,but none of those could be securely associated with any confirmed black hole-black hole merger event.Based on this first experience and the near future technical improvements of our network system,we will be more competitive in detecting the optical counterparts from some GW events that will be identified during the upcoming O3 run,especially those emerging from binary neutron star mergers.展开更多
We study the electromagnetic radiation from a newborn magnetar whose magnetic tilt angle decreases rapidly. We calculate the evolution of the angular spin frequency, the perpendicular component of the surface magnetic...We study the electromagnetic radiation from a newborn magnetar whose magnetic tilt angle decreases rapidly. We calculate the evolution of the angular spin frequency, the perpendicular component of the surface magnetic field strength, and the energy loss rate through magnetic dipole radiation. We show that the spin-down of the magnetar experiences two stages characterized by two different timescales. The apparent magnetic field decreases with the decrease of the tilt angle. We further show that the energy loss rate of the magnetar is very different from that in the case of a fixed tilt angle. The evolution of the energy loss rate is consistent with the overall light curves of gamma-ray bursts which show a plateau structure in their afterglow stage. Our model supports the idea that some gamma-ray bursts with a plateau phase in their afterglow stage may originate from newborn millisecond magnetars.展开更多
The redshift and luminosity distributions of 36 Swift short gamma-ray bursts(GRBs) are fitted by connecting their event rates with cosmic star formation rates using power-law distributed delay times f(τ) ∝τ-1, wher...The redshift and luminosity distributions of 36 Swift short gamma-ray bursts(GRBs) are fitted by connecting their event rates with cosmic star formation rates using power-law distributed delay times f(τ) ∝τ-1, where a broken-power-law luminosity function is assumed and some empirical observational selection effects are taken into account. As a result, the most-likely model parameters are constrained to be ν1 = 0.91, ν2 = 1.66 as power-law indices, with a break at Lb= 2.51 × 1051 erg s-1 for the luminosity function and τc= 6.0 Gyr for a typical gravitational wave decay timescale of the binary orbit. The corresponding local rate of short GRBs is found to be 3-4 Gpc-3 yr-1. With these parameters, the detectable numbers of short GRBs are estimated within the horizon of Advanced LIGO.展开更多
基金supported by the National SKA Program of China(2020SKA0120100)supported by NSFC grant No.12203017。
文摘Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.
基金supported by the National Key R&D Program of China(2021YFA0718500,2022YFF0711404)the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(grant Nos.XDA15360300,XDA15052700 and E02212A02S)+1 种基金the National Natural Science Foundation of China(grant Nos.U2031205,12133007)supported by the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences,grant No.XDA15360000。
文摘Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM),consisting of two microsatellites,is designed to detect gamma-ray bursts associated with gravitational-wave events.Here,we introduce the real-time burst alert system of GECAM,with the adoption of the BeiDou-3 short message communication service.We present the post-trigger operations,the detailed ground-based analysis,and the performance of the system.In the first year of the in-flight operation,GECAM was triggered by 42 gamma-ray bursts.The GECAM real-time burst alert system has the ability to distribute the alert within~1 minute after being triggered,which enables timely follow-up observations.
基金supported by the National SKA Program of China(Nos.2020SKA0120300,2020SKA0120100)the Outstanding Young and Middle-aged Science and Technology Innovation Teams from Hubei colleges and universities(No.T2021026)the Young Top-notch Talent Cultivation Program of Hubei Province,and the Key Laboratory Opening Fund(MOE)of China(grant No.QLPL2021P01)。
文摘Strangeon stars,which are proposed to describe the nature of pulsar-like compact stars,have passed various observational tests.The maximum mass of a non-rotating strangeon star could be high,which implies that the remnants of binary strangeon star mergers could even be long-lived massive strangeon stars.We study rigidly rotating strangeon stars in the slowly rotating approximation,using the Lennard-Jones model for the equation of state.Rotation can significantly increase the maximum mass of strangeon stars with unchanged baryon numbers,enlarging the mass-range of long-lived strangeon stars.During spin-down after merger,the decrease of radius of the remnant will lead to the release of gravitational energy.Taking into account the efficiency of converting the gravitational energy luminosity to the observed X-ray luminosity,we find that the gravitational energy could provide an alternative energy source for the plateau emission of X-ray afterglow.The fitting results of X-ray plateau emission of some short gamma-ray bursts suggest that the magnetic dipole field strength of the remnants can be much smaller than that of expected when the plateau emission is powered only by spin-down luminosity of magnetars.
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 Natural Science Foundation of China(NSFC,Grant No.12203013)the Guangxi Science Foundation(grant Nos.2023GXNSFBA026030and Guike AD22035171)。
文摘In this paper,we upgrade the constraints for the Earth-mass primordial black hole mergers model based on the first Canadian Hydrogen Intensity Mapping Experiment(CHIME)/fast radio burst(FRB)catalog.Assuming the null hypothesis that the observed non-repeating FRBs originate from Earth-mass primordial black hole mergers,we find that how the charges were distributed in the primordial black hole population is well described by a double powerlaw function with typical charge value of law function with typical charge value of q_(c)/10^(-5)=1.60_(-0.28)^(+0.28),where the power-law index α_(1)=2.33_(-0.18)^(+0.15) for q<q_(c) and α_(2)=4.56_(-0.26)^(+0.30)for q≥q_(c).Here,q represents the charge of the black hole in units of√GM,where M is the mass of the black hole.Furthermore,we infer the local event rate of the bursts is 8.8_(-2.1)^(+5.7)×10^(4)Gpc^(-3) yr^(-1),which indicates that an abundance of the primordial black hole population f■10^(-4) is needed to account for the observed FRBs by CHIME.The results of this paper lay the basis for further research on the electromagnetic radiation background generated by the merger of primordial black hole mergers.
基金supported by the National Key R&D Program of China(2021YFA0718500)support from the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(grant Nos.XDA15360102,XDA15360300,XDA15052700 and E02212A02S)+1 种基金the National Natural Science Foundation of China(grant Nos.12173038 and U2038106)the National HEP Data Center(grant No.E029S2S1)。
文摘Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations.Localization based on the relative counts of different detectors has been widely used for all-sky gamma-ray monitors.There are two major methods for this count distribution localization:χ^(2)minimization method and the Bayesian method.Here we propose a modified Bayesian method that could take advantage of both the accuracy of the Bayesian method and the simplicity of the χ^(2)method.With comprehensive simulations,we find that our Bayesian method with Poisson likelihood is generally more applicable for various bursts than the χ^(2)method,especially for weak bursts.We further proposed a location-spectrum iteration approach based on the Bayesian inference,which could alleviate the problems caused by the spectral difference between the burst and location templates.Our method is very suitable for scenarios with limited computation resources or timesensitive applications,such as in-flight localization software,and low-latency localization for rapidly follow-up observations.
基金supported by the Strategic Priority Program on Space Science,the Chinese Academy of Sciences,grant Nos.XDA15360102,XDA15360300 and E02212A02Sthe National Natural Science Foundation of China(Project:12061131007)。
文摘The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM)mission is designed to monitor the Gamma-Ray Bursts(GRBs)associated with gravitational waves and other high-energy transient sources.The mission consists of two microsatellites which are planned to operate at the opposite sides of the Earth.Each GECAM satellite could detect and localize GRBs in about 8 keV-5 MeV with its 25 Gamma-Ray Detectors(GRDs).In this work,we report the in-flight energy calibration of GRDs using the characteristic gamma-ray lines in the background spectra,and show their performance evolution during the commissioning phase.Besides,a preliminary cross-calibration of energy response with Fermi GBM data is also presented,validating the energy response of GRDs.
基金supported by the National Key R&D Program of China(2021YFA0718500)from the Minister of Science and Technology of China(MOST)supports from the National Natural Science Foundation of China under grants 12173103,12003028,U2038101,U2038102 and 11733009+2 种基金supported by International Partnership Program of Chinese Academy of Sciences(grant No.113111KYSB20190020)the National SKA Program of China(2022SKA0130100)the China Manned Spaced Project(CMS-CSST-2021-B11)。
文摘Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154suggests that at least some FRBs can be generated by magnetars.However,the majority of X-ray bursts from magnetars are not associated with radio emission.The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs.Here we report long time spin evolution of SGR J1935+2154 until the end of 2022.According to v and v,the spin evolution of SGR J1935+2154 could be divided into two stages.The first stage evolves relatively steady evolution until 2020 April 27.After the burst activity in2020,the spin of SGR J1935+2154 shows strong variations,especially for v.After the burst activity in 2022October,a new spin-down glitch with△v/v=(-7.2±0.6)×10^(-6)is detected around MJD 59876,which is the second event in SGR J1935+2154.At the end,spin frequency and pulse profile do not show variations around the time of FRB 200428 and radio bursts 221014 and 221021,which supply strong clues to constrain the trigger mechanism of FRBs or radio bursts.
基金supported by operating grants from the National Science and Engineering Research Council of Canada(NSERC)
文摘By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.In our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding medium.Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but phenomenological.FRB-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel instability.Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently.The resulting emission frequency,luminosity and duration in our model are consistent with FRB data.We find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB(SGRB) with fits to BAT/XRT light curves.
基金Supported by the National Natural Science Foundation of China
文摘The well-known correlation between radio luminosity （LR） and X-ray luminosity （Lx）, LR/LX 10^-5, holds for a variety of objects, such as active galactic nuclei, Galactic black holes, solar flares and cool stars. Here we extend the relation to gamma-ray bursts （GRBs） and find that the GRBs also obey a similar LR - LX relation, with a slightly different slope of LR ∝ LX^1.1. This relation implies that the explosions that occur on different scales may have a common underlying origin.
基金the National Natural Science Foundation of China(Grant Nos.11533003,11851304 and U1731239)Guangxi Science Foundation and special funding for Guangxi distinguished professors(2017AD22006)。
文摘High energy photon radiations of gamma-ray bursts(GRBs)and active galactic nuclei(AGNs)are dominated by their jet radiations.We examine whether the synchrotron radiations of jets in BL Lacs,flat spectrum radio quasars(FSRQs),and Narrow Line Seyfert 1 galaxies(NLS1s)follow the relation between the prompt gamma-ray emission and the initial Lorentz factor(Γ0)of GRBs.It is shown that the AGN sample does not agree with the Lp-Ep,z-Γ0 relation of GRBs.In addition,we obtain a tight relation of Lsyn∝Е0.45±0.15δ3.50±0.25 syn,p for FSRQs and NLS1 galaxies,where Lsyn is the luminosity at peak photon energy Esyn,p of the synchrotron radiations.This relation is different from the Lp-Ep,z-Γ0 relation of GRB s.The dependence of Lsyn toδis consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies,but it is not for GRBs.We argue thatΓ0 may be a representative of the kinetic power of the radiating region and the tight Lp-Ep,z-Γ0 relation is shaped by the radiation physics and the jet power together.
基金supported by the National Basic Research Program of China(973 Program,Grant 2014CB845800)the National Natural Science Foundation of China(Grant Nos.11773010,U1431124 and U1738132)
文摘The relativistic external shock model of gamma-ray burst （GRB） afterglows has been estab- lished with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ee and for the magnetic field eB, the number density of the environment n and the index of the power- law distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as： the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. In this paper, by as- suming all four parameters （except p） change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.
文摘The Swift/XRT detected the X-ray afterglow of long burst GRB 220117A,which began to rebrighten 300 s after triggering and followed a single power-law decay segment after thousands of seconds of the orbital observation gap.This segment is different from the shallow decay segment(plateau)and flare,and may belong to a giant X-ray bump.We investigated this segment by the fall-back accretion model and found that the model can interpret this segment with reasonable parameter values.Within this physical model scenario,the fall-back accretion rate reaches a peak value~1.70×10~(-5)M_⊙s~(-1)around 300 s in the central engine frame,which is compatible with the late mass supply rate of some low-metallicity massive progenitor stars.The initial black hole(BH)spin is a_0=0.64_(-0.26)~(+0.24)and implies that this re-brightening signature requires a larger BH spin.The total accretion mass during the fall-back process is M_(acc)=(3.09±0.02)×10~(-2)M_⊙.The jet energy from the fall-back accretion is(9.77±0.65)×10~(52)erg,with a ratio of 0.066 to the isotropic-equivalent radiation energies of the GRB prompt phase in the 1-10~4 keV band.The fall-back radius r_p corresponding to the peak time of fall-back t_p is(3.16±0.05)×10~(10)cm,which is consistent with the typical radius of Wolf-Rayet stars.In summary,our results provide additional support for the origin of the long burst from the core collapse of Wolf-Rayet stars,and its late central engine activity is likely due to the fall-back accretion process.
基金supported by the National Natural Science Foundation of China (grant No. U2038106)China Manned Spaced Project (CMS-CSST-2021-A12)+1 种基金supported by the National Natural Science Foundation of China(grant No. 12203013)the Guangxi Science Foundation(grant Nos. AD22035171 and 2023GXNSFBA026030)。
文摘The physical mechanism of fast radio bursts(FRBs) is still unknown. On 2020 April 28, a special radio burst, FRB200428, was detected and believed to be associated with the Galactic magnetar SGR 1935+2154. It confirms that at least some of the FRBs were generated by magnetars, although the radiation mechanism continues to be debated.To this end, we study in detail the multiband afterglows of FRB 200428 described by the synchrotron fireball shock model. We find the prediction for the optical and radio afterglows of FRB 200428 is consistent with the observations when considering the post-FRB optical and radio upper limits from the literature. We also show that the follow up detection of the afterglows from fast radio bursts like—FRB 200428 is possible at the radio band,though challenging. Based on our model, one can obtain information about the energy of the fireball, the radiation zone, and the nature of the surrounding medium. That may shed light on the physical mechanism of FRBs.
基金supported by the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences,grant XDB0550401supported by the National Natural Science Foundation of China(NSFC,grant No.12173009)+2 种基金by the Natural Science Foundation of Guangxi(2020GXNSFDA238018)by the Bagui Young Scholars Programsupported by the National Postdoctoral Program for Innovative Talents(grant No.GZB20230765)。
文摘In spite of the importance of studying the cosmic generation of heavy elements through the r-process,the detection of a kilonova resulting from the merger of a neutron star binary is still a challenging task.In this paper,we show that the Visible Telescope(VT)onboard the ongoing SVOM space mission is powerful for identifying kilonova candidates associated with short gamma-ray bursts up to a distance of 600 Mpc.A significant color variation,turning blue and then turning red,is revealed by calculating the light curves in both red and blue channels of VT by a linear combination of an afterglow and an associated kilonova.The maximum color variation is as high as~0.5-1 mag,which is far larger than the small photometry error of~0.2 mag of VT for a point source with a brightness of 23 mag.Up to a distance of 600 Mpc,~1-2 kilonova candidates per year are predicted to be identified by VT.
基金the National Natural Science Foundation of China.
文摘A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.
基金supported by the National Natural Science Foundation of China(Grant Nos.11533003,11673006,U1331202,U1931133 and U1938201)the Guangxi Science Foundation(2016GXNSFFA380006,AD17129006and 2018GXNSFGA281007)+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB23040000)the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences(XDA15052600)financial support from the Chinese Academy of Sciences PIFI post-doctoral fellowship program(program C)financial support of the Univ Earth S Labex program at Sorbonne Paris Cité(ANR-10-LABX-0023 and ANR-11-IDEX-0005-02)
文摘The second(O2)observational campaign of gravitational waves(GWs)organized by the LIGO/Virgo Collaborations has led to several breakthroughs such as the detection of GW signals from merger systems involving black holes or neutrons stars.During O2,14 GW alerts were sent to the astronomical community with sky regions mostly covering over hundreds of square degrees.Among them,six were finally confirmed as real astrophysical events.Since 2013,a new set of ground-based robotic telescopes called Ground-based Wide Angle Camera system(GWAC)project and its pathfinder mini-GWAC has been developed to contribute to the various challenges of multi-messenger and time domain astronomy.The GWAC system is built up in the framework of the ground-segment system of the SVOM mission that will be devoted to the study of the multi-wavelength transient sky in the next decade.During O2,only the mini-GWAC telescope network was fully operational.Due to the wide field of view and fast automatic follow-up capabilities of the mini-GWAC telescopes,they were adept to efficiently cover the sky localization areas of GW event candidates.In this paper,we present the mini-GWAC pipeline we have set up to respond to GW alerts and we report our optical follow-up observations of eight GW alerts detected during the O2 run.Our observations provided the largest coverage of the GW localization areas with a short latency made by any optical facility.We found tens of optical transient candidates in our images,but none of those could be securely associated with any confirmed black hole-black hole merger event.Based on this first experience and the near future technical improvements of our network system,we will be more competitive in detecting the optical counterparts from some GW events that will be identified during the upcoming O3 run,especially those emerging from binary neutron star mergers.
基金Supported by the National Natural Science Foundation of China
文摘We study the electromagnetic radiation from a newborn magnetar whose magnetic tilt angle decreases rapidly. We calculate the evolution of the angular spin frequency, the perpendicular component of the surface magnetic field strength, and the energy loss rate through magnetic dipole radiation. We show that the spin-down of the magnetar experiences two stages characterized by two different timescales. The apparent magnetic field decreases with the decrease of the tilt angle. We further show that the energy loss rate of the magnetar is very different from that in the case of a fixed tilt angle. The evolution of the energy loss rate is consistent with the overall light curves of gamma-ray bursts which show a plateau structure in their afterglow stage. Our model supports the idea that some gamma-ray bursts with a plateau phase in their afterglow stage may originate from newborn millisecond magnetars.
基金supported by the National Natural Science Foundation of China(Grant Nos.11473008, 11822302 and 11833003)the Fundamental Research Funds for the Central Universities(Grant No. CCNU18ZDPY06)
文摘The redshift and luminosity distributions of 36 Swift short gamma-ray bursts(GRBs) are fitted by connecting their event rates with cosmic star formation rates using power-law distributed delay times f(τ) ∝τ-1, where a broken-power-law luminosity function is assumed and some empirical observational selection effects are taken into account. As a result, the most-likely model parameters are constrained to be ν1 = 0.91, ν2 = 1.66 as power-law indices, with a break at Lb= 2.51 × 1051 erg s-1 for the luminosity function and τc= 6.0 Gyr for a typical gravitational wave decay timescale of the binary orbit. The corresponding local rate of short GRBs is found to be 3-4 Gpc-3 yr-1. With these parameters, the detectable numbers of short GRBs are estimated within the horizon of Advanced LIGO.
