# 28th Texas Symposium on Relativistic Astrophysics

13-18 December 2015
International Conference Centre Geneva
Europe/Zurich timezone

## Short gamma-ray bursts from binary neutron star mergers: the time-reversal scenario

15 Dec 2015, 14:00
21m
Level 2, Room 7&8 (International Conference Centre Geneva)

### Level 2, Room 7&8

#### International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva

### Speaker

Dr Riccardo Ciolfi (University of Trento and INFN-TIFPA)

### Description

Leading models relate short gamma-ray bursts (SGRBs) to a relativistic jet launched by the black hole (BH)-accretion torus system that can be formed in a binary neutron star (BNS) or a NS-BH binary merger. However, recent observations by Swift have revealed a large fraction of SGRB events accompanied by X-ray afterglows with durations $\sim10^2-10^5$ s, suggesting continuous energy injection from a long-lived central engine that is incompatible with the short ($<\!1$ s) accretion timescale of a BH-torus system. The formation of a supramassive NS (SMNS), resisting the collapse on much longer spin-down timescales, can explain these X-ray afterglows as powered by the magnetic spin-down of the star, but leaves serious doubts on whether a relativistic jet can be launched at merger. Here we present a novel "time-reversal" scenario that can solve this dichotomy. In this scenario, the SGRB is produced *after* the eventual collapse of the SMNS to a BH, but observed *before* part of the long-lasting X-ray signal powered by magnetic spin-down.

### Primary author

Dr Riccardo Ciolfi (University of Trento and INFN-TIFPA)

### Co-author

Mr Daniel Siegel (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))