Constraining properties of GRB central engines with X-ray flares

X-ray flares in gamma-ray bursts (GRBs) are believed to be generated by the late activities of central engine, and thus provide an useful tool to diagnose the properties of central objects. In this paper, we work on a GRB X-ray flare sample whose bulk Lorentz factors are constrained by two different methods and the jet opening angles are determined by the jet breaks in afterglow light curves. Considering a hyperaccreting stellar-mass black hole (BH) as the central engine of GRBs and the Blandford & Znajek process (BZ) as the jet production mechanism, we constrain the parameters of central engine by using the X-ray flare data. We find that the BZ mechanism is so powerful making it possible to interpret both GRB prompt emissions and bright X-ray flares. The wind parameter (p) and accreted mass (M-d) fall into reasonable ranges. Our result is also applied to GRB 170817A. The late X-ray flare in GRB 170817A, if it is true, might not be a BH origin.

Automated summary

The X-ray flares in gamma-ray bursts are believed to be generated by the late activities of central engine, providing a useful tool to diagnose the properties of central objects. By studying a sample of GRB X-ray flares, the parameters of the central engine were constrained, and the jet opening angles were determined. It was found that the Blandford & Znajek process can explain both GRB prompt emissions and bright X-ray flares, but the X-ray flare in GRB 170817A may not be of black hole origin.