X-ray Constraints On The Gamma Ray Burst Center Engine

Gamma Ray Burst(GRB)is a burst of high-energy photons in the universe within short time scale.The X-ray afterglow contains a large number of center engine information.We attempted to analyze the X-ray afterglow light curves to limit the physical parameters of the GRB center engine.In 2019,Piro et al.claimed that a X-ray variability around 160 days post-merger for GW170817/GRB 170817A.We conducted a statistical correlation study on this X-ray variability and the X-ray variability of GRB170817A seems shared the similar properties with the X-ray flares observed in GRB afterglow.We discuss the feasibility of using four theoretical models to explain the X-ray variability of GRB 170817A(stable NS,long-lived super-massive NS,BH)and parametric analysis of the results.The X-ray variability can be produced by the ejection of the magnetosphere from a supra-massive neutron star collapsing into a black hole.This indicates that the remnants of binary neutron star merger is likely to be a long-lived super-mass neutron star,and the minimum surface magnetic field of the long-lived super-massive neutron star is B_P?5.25×10¹³G.For re-brightening in GRB afterglow,we statistics the data of Swift which have bump in X-ray afterglow from 2005 to 2020 May.According to our data analysis,the re-brightening of GRB afterglow has a bi-modal distribution,with the peaks appearing near t_b1=1578.27 s and t_b2=16230.43 s.We suspect that the early re-brightening in GRB afterglow may be due to forward shock and the late re-brightening in the GRB afterglow is likely to be the re-activity of the neutron star central engine,and we use the neutron star fallback accretion model combined with the forward shock model to explain the late re-brightening.Through MCMC fitting,we get forward shock model can explain the early re-brightening and the fallback accretion of the neutron star may be the physical origin of the late re-brightening in the GRB afterglow.