| Gamma-ray bursts(GRB s)are the most powerful bursts in the universe.They have the characteristics of high energy,strong burst and instantaneous.Typical photon energy distributions range from tens of KeV to several MeV,and isotropic luminosity can reach～1051-1052 erg s-1.The transient radiation process of a gamma-ray burst is short and intense,and can be explained by the fireball-internal shock model,but the type of central engine of the reaction gamma-ray burst is still not fully determined because it is difficult to capture direct evidence of the type of central engine.Some special radiation phenomena,such as X-ray flare,platform radiation and malleable radiation,which occur in the afterglow phase of the burst,are related to the activity of the central engine of the gamma-ray burst.So using these particular components of radiation can help us examine and limit the type of gamma-burst center engine.Our work is based on a large sample of observational data,especially involving the main evidence of sustained activity of the gamma-burst central engine,such as the flare phenomenon and platform radiation,to test the central engine model of the gamma-burst and analyze the energy distribution of the different stages of the gammaburst.The main content of this paper is introduced as follows:Long-duration gamma-ray bursts(GRBs)are generally related to the core-collapse of massive stars.In the collapsar scenario,a rotating stellar-mass black hole(BH)surrounded by a hyperaccretion disk has been considered as one of the plausible candidates of GRB central engines.In this paper,we work on a sample including 146 long GRB s with significant jet break features in the multiband afterglows.The jet opening angles can then be obtained by the jet break time.By assuming GRB jets powered by the Blandford-Znajek(BZ)mechanism in the BH hyperaccretion system,we analyze the distributions of the long GRB luminosities and durations in the samples,and constrain the accretion rates for the different BH spins.As a result,we find that the BZ mechanism is so powerful that it is possible to interpret the long GRB prompt emissions within reasonable accretion rates.Distinct X-ray plateau and flare phases have been observed in the afterglows of gammaray bursts(GRBs),and most of them should be related to central engine activities.In this paper,we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares.There are 51 GRBs that overlap in the two selected samples.We analyze the distributions of the proportions of the plateau energy Eplateau and the flare energy Eflare relative to the isotropic prompt emission energy Eγ,iso.The results indicate that they well meet the Gaussian distributions and the medians of the logarithmic ratios are～-0.96 and-1.39 in the two cases.Moreover,strong positive correlations between Eplateau(or Eflare)and Eγ,iso with slopes of～0.95(or～0.80)are presented.For the overlapping sample,the slope is～0.80.We argue that most of X-ray plateaus and flares might have the same physical origin but appear with different features because of the different circumstances and radiation mechanisms.We also test the applicabilities of two models,i.e.,black holes surrounded by fractured hyperaccretion disks and millisecond magnetars,on the origins of X-ray plateaus and flares.The multi-band afterglow of gamma-burst with power-law attenuation fits well with the fireball-outer shock model.Our work also extends the standard afterglow model of gammaray bursts to the field of fast radio bursts,and estimates the intensity of the afterglow of the source fast radio burst FRB 200428.Fast radio bursts(FRB s)are a new type of short intense radio pulses.Although relatively abundant samples have been found,their afterglow radiation is still not found.On April 28,2020,a special radio burst,FRB 200428,was detected from the galactic magnetar SGR 1935+2154.The discovery confirms that at least some FRBs are produced by magnetars,although the radiation mechanism is still debated.To this end,we use the synchronous external shock wave model to study in detail the intensity of multi-band afterglow radiation of FRB 200428 and its detection possibility,which can provide reference for us to observe similar samples in the future.Through this work,we find that the prediction of the optical and radio afterglow of FRB 200428 is consistent with the observation results,taking into account the upper limit of the optical and radio afterglow observed in the literature.We also show that it is possible,albeit challenging,to track and detect the afterglow of fast radio bursts such as FRB 200428 in the radio band.Based on our model,we can obtain relevant information about the energy of the fireball,the radiation region and the properties of the surrounding medium.This may shed light on the physics of fast radio bursts.Finally,the above research work is summarized,and the two hot issues of gamma-ray bursts and fast radio bursts are prospected.Hopefully,with more detection equipment,we’ll be able to capture more information that will allow us to unravel the mysteries of these highenergy transient radiation processes. |
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