Constraining Properties of GRB Central Engines with X-ray flares

TL;DR

This study uses X-ray flares in gamma-ray bursts to probe the properties of their central engines, suggesting the Blandford-Znajek process can power both prompt emissions and flares, with implications for specific GRBs like 170817A.

Contribution

It constrains central engine parameters using X-ray flare data and supports the BZ mechanism as a common power source for GRB emissions and flares.

Findings

BZ mechanism can power both prompt emissions and bright X-ray flares.

The wind parameter and accreted mass are within reasonable ranges.

The late X-ray flare in GRB 170817A may not originate from a black hole.

Abstract

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 lightcurves. 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.