Giant flares(GFs)are unusual bursts from soft gamma-ray repeaters(SGRs)that release an enormous amount of energy in a fraction of a second.The afterglow emission of these SGR-GFs or GF candidates is a highly beneficia...Giant flares(GFs)are unusual bursts from soft gamma-ray repeaters(SGRs)that release an enormous amount of energy in a fraction of a second.The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition,relativistic speed and emission mechanisms.GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc.In this work,we searched for transient gamma-ray emission in past observations by Fermi-LAT in the direction of GRB 200415A.These observations confirm that GRB 200415A is observed as a transient GeV source only once.A pure pair-plasma fireball cannot provide the required energy for the interpretation of GeV afterglow emission and a baryonic poor outflow is additionally needed to explain the afterglow emission.A baryonic rich outflow is also viable,as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks.Using the peak energy(Ep)of the time-resolved prompt emission spectra and their fluxes(Fp),we found a correlation between Ep and Fp or isotropic luminosity Liso for GRB 200415A.This supports the intrinsic nature of Ep-Liso correlation found in SGRs-GFs,hence favoring a baryonic poor outflow.Our results also indicate a different mechanism at work during the initial spike,and that the evolution of the prompt emission spectral properties in this outflow would be intrinsically due to the injection process.展开更多
基金support by the Fundamental Research Funds for the Central Universities(14380035)supported by National Key Research and Development Programs of China(2018YFA0404204)+3 种基金the National Natural Science Foundation of China(Grant Nos.11833003,U1838105 and U1831135)the Program for Innovative Talents,Entrepreneur in Jiangsuthe Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(Grant No.XDB23040400)BRICS grant DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G)for the financial support。
文摘Giant flares(GFs)are unusual bursts from soft gamma-ray repeaters(SGRs)that release an enormous amount of energy in a fraction of a second.The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition,relativistic speed and emission mechanisms.GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc.In this work,we searched for transient gamma-ray emission in past observations by Fermi-LAT in the direction of GRB 200415A.These observations confirm that GRB 200415A is observed as a transient GeV source only once.A pure pair-plasma fireball cannot provide the required energy for the interpretation of GeV afterglow emission and a baryonic poor outflow is additionally needed to explain the afterglow emission.A baryonic rich outflow is also viable,as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks.Using the peak energy(Ep)of the time-resolved prompt emission spectra and their fluxes(Fp),we found a correlation between Ep and Fp or isotropic luminosity Liso for GRB 200415A.This supports the intrinsic nature of Ep-Liso correlation found in SGRs-GFs,hence favoring a baryonic poor outflow.Our results also indicate a different mechanism at work during the initial spike,and that the evolution of the prompt emission spectral properties in this outflow would be intrinsically due to the injection process.
