The Investigation Of Long-lasting Activity Of Central Engine For Gamma-ray Bursts

During the postgraduate period,my work is mainly investigating the long-lasting activity of central engine for gamma-ray burst,and the magnetic dipole(MD)and gravitational wave(GW)radiations for magnetar as the central engine of gamma-ray bursts.The results are as follows:We have presented a systematic search for the long GRBs with two-episode prompt emission and the short GRBs with extended emission(EE)observed with Fermi/GBM.There are no correlations between the duration and the quiescent time.We do not find significant differences for the spectral parameters of two-episode.This suggests that the two-episode emission components may share the same physical origin.For the short GRBs with EE,we find that The peak energy of EE in our sample are usually softer than the initially hard spike episode.However,the total fluence of the hard spike and followed EE are comparable with each other.Moreover,Both peak energy and average flux of short GRBs with EE in our sample are not significant difference with other short GRBs as well as GRB 170817A.Those results suggest that the short GRBs with EE in our sample are likely shared similar physical origin.A magnetar is thought to be central engine of some long GRBs with X-ray plateau.We first investigate the temporal evolution behavior of X-ray afterglow during the spin-down of magnetar.We show that the EM emission light curve of the MD radiation is described as L ?(1 + t/?c)?,and a=-1 in the GW emission dominated scenario and ?=-2 in the MD radiation dominated scenario.Transition from a GW emission dominated epoch to an MD radiation dominated epoch may show up as a smooth break with a decaying slope from-1 to-2.Next,we constrain the braking index and energy partition of magnetar spin-down with Swift/XRT data.We find that the braking indices are neither close to 3 nor 5,but range between these two values.It is likely a normal distribution with the center value nc=4.02 ± 0.11,the distribution of braking indices of our sample is much larger than the distribution of pulsar braking indices.Given the initial parameters(PO = 3 ms,?=0.01 or ?= 0.005),the distributions of R tend to normal with center values Rc=0.47 ± 0.09(?=0.005)and Rc=0.12 ± 0.04(? = 0.01),respectively.Moreover,there seems to be an anticorrelation between R and n.It indicates that a higher braking index tends to give rise to GW dominated radiation for magnetar spin-down.We systematically study a sample of 20 GRB/SN association systems.By deriving/collecting basic physical parameters of GRBs and SN and analyzing their correlations,and finally discussed the energy partition and the case of a magnetar central engine.We find that the peak brightness,56Ni mass and explosion energy of the SN in our sample are systematically higher than other Type Ib/c SN.Moreover,the beaming-corrected GRB y-ray energy and kinetic energy in our sample are both less than the maximum available energy of a millisecond magnetar.When aspherical explosions are assumed,most SN in our sample are below the energy budget limit of a magnetar.The total GRB+SN energy of most systems in our sample are below or close to the maximum rotation energy of a magnetar when assuming aspherical SN explosions.Those evidence indicate that most GRB/SN associated events in our sample can be driven by a millisecond magnetar.The energy partition between GRB and SN in these systems is such that most of the energy is carried by the SN.The GRB energy is typically less than 30%.