Reviewing the case of the atypical central-engine activity in GRB 110709B

TL;DR

This paper analyzes the atypical GRB 110709B, proposing a multi-phase central-engine model involving a protomagnetar, black hole formation, and a Blandford-Znajek engine, successfully explaining its complex light curve and afterglow.

Contribution

It introduces a novel multi-phase central-engine model for GRB 110709B, linking each observed peak to distinct astrophysical processes.

Findings

The model explains the three peaks in the light curve.

It successfully reproduces observed timescales and fluxes.

The afterglow is consistent with the standard fireball model.

Abstract

The unusual GRB 110709B triggered Swift/BAT twice, with a time difference of $\sim 11$ minutes. Its light curve presented three noticeable peaks but only two were originally identified. In this work, we describe each peak as due to a different central-engine phase: the first one is the millisecond-protomagnetar stage, the second one is the BH-formation collapse phase and the last one is the Collapsar scenario with a Blandford-Znajek engine. Additionally, we analyze and explain the afterglow phase evoking the standard fireball model. Our model can successfully describe the timescales, fluxes and spectral indices observed for GRB 110709B.