Signature of a New-Born Black Hole from the Collapse of a Supra-massive Millisecond Magnetar

TL;DR

This paper presents evidence of a new-born black hole following a magnetar collapse in a gamma-ray burst, supporting the magnetar central engine model and offering insights into the properties of both the magnetar and black hole.

Contribution

It identifies observational signatures indicating the formation of a black hole after a magnetar in a GRB, providing new evidence for the magnetar central engine hypothesis.

Findings

GRB 070110 shows a small X-ray bump after the plateau.

The plateau is explained by a spin-down supra-massive magnetar.

The X-ray bump is interpreted as fall-back black hole accretion.

Abstract

The X-ray plateau followed by a steep decay ("internal plateau") has been observed in both long and short gamma-ray burst (GRBs), implying a millisecond magnetar operating in some GRBs. The sharp decay at the end of plateau, marking the abrupt cessation of the magnetar central engine, has been considered as the collapse of a supra-massive magnetar to a black hole (BH) when it spins down. If "internal plateau" is indeed the evidence of a magnetar central engine, a natural expectation is a signature from the new-born BH in some candidates. In this work, we find that GRB 070110 is a particular case, which shows a small X-ray bump following its "internal plateau". We interpret the plateau with a spin-down supra-massive magnetar and the X-ray bump with a fall-back BH accretion. This indicates that the new-born BH is likely active in some GRBs. Therefore, GRB 070110-like events may provide a further support to the magnetar central engine model and enable us to investigate the properties of the magnetar as well as the new-born BH.