Hyperaccretion after the Blandford-Znajek Process: a New Model for GRBs with X-Ray Flares Observed in Early Afterglows

TL;DR

This paper introduces a three-stage model combining Blandford-Znajek and hyperaccretion processes to explain early afterglows and X-ray flares in Gamma-Ray Bursts, linking black hole energy extraction with magnetic instabilities.

Contribution

It presents a novel three-stage model that integrates BZ and hyperaccretion processes to interpret early GRB afterglows and X-ray flares, advancing understanding of central engine dynamics.

Findings

The model explains the energies and timescales of GRBs with X-ray flares.

It links magnetic energy accumulation to flare onset.

The three-stage process aligns with observed early afterglow features.

Abstract

We propose a three-stage model with Blandford-Znajek (BZ) and hyperaccretion process to interpret the recent observations of early afterglows of Gamma-Ray Bursts (GRBs). In the first stage, the prompt GRB is powered by a rotating black hole (BH) invoking the BZ process. The second stage is a quiet stage, in which the BZ process is shut off, and the accretion onto the BH is depressed by the torque exerted by the magnetic coupling (MC) process. Part of the rotational energy transported by the MC process from the BH is stored in the disk as magnetic energy. In the third stage, the MC process is shut off when the magnetic energy in the disk accumulates and triggers the magnetic instability. At this moment, the hyperaccretion process may onset, and the jet launched in this restarted central engine generates the observed X-ray flares. This model can account for energies and timescales of GRBs with X-ray flares observed in early afterglows.