The Study Of Central Engine:the Multi-band Afterglow Of GRB 151027A Powered By Neutron Star And Black Hole

The origin of gamma-ray bursts(GRB)are related to either the death of massive stars or the merge of two compact stars.The progenitors of gamma-ray bursts have been widely discussed.However,the central engines of individual GRBs are different and complex.Although current observations of GRB afterglow are abundant compared to early days,the multi-band observation data still seem to be lacked for some GRBs that the central engines couldn't be determined easily.Therefore,detailed discussions and analysis are needed for those GRBs.Based on some of the most discussed models of GRBs,the approach of constraining the central engine is to use the observational characteristics which are predicted in those models,and match them with the observed multi-band afterglow of GRBs.A serial of comprehended analysis is conducted based on the multi-band afterglow observations of GRB 151027A and its possible central engine is discussed.The X-ray afterglow of this burst is detected by Swift/XRT shows that there are two plateaus in the light curve.At the end of the first plateau,there is a sharp decay which could be a strongly evidence for the presents of a rapidly spinning and strongly magnetized neutron star(NS).The second X-ray plateau lasts for more than 104 s which could be interpreted by the fall-back accretion of black hole(BH).Both of two plateaus have distinct features indicating that the afterglow of GRB 151027A is powered by a NS which then collapse to BH.Meanwhile the i-band afterglow detected by P60 has two broad bumps,which can be well explained by the superposition of external shock and the black hole fall-back accretion which is consisted with the scenario of NS collapsing to BH.We first present a detailed review in Chapter 1,include the basic images,observational results and the theory of GRB.Chapter 2 mainly introduces two types model of the GRB central engine,which are the Millisecond Magnetars and Hyper-Accreting Black Holes.In Chapter 3 we describe the multiwavelength observational features of GRB 151027A and propose our model fitting the light curve.Finally,we present a summary of my work and the expectation for the future.