Central Engine-Powered Bright X-ray Flares in Short Gamma-Ray Bursts: A Hint of Black Hole-Neutron Star Merger?

TL;DR

This paper suggests that bright X-ray flares in short gamma-ray bursts could indicate black hole-neutron star mergers, based on observational data and theoretical considerations about fallback material and accretion disks.

Contribution

It proposes a novel link between bright X-ray flares and BH-NS mergers, supported by observational analysis of Swift data and theoretical reasoning.

Findings

Three short bursts show bright X-ray flares.

Two of these flares are likely related to central engine reactivity.

The proposed link can be tested with future gravitational wave detections.

Abstract

Short gamma-ray bursts may originate from the merger of double neutron stars (NS) or that of a black hole (BH) and an NS. We propose that the bright X-ray flare related to the central engine reactivity may hint a BH-NS merger, since such a merger can provide more fall-back materials and therefore a more massive accretion disk than the NS-NS merger. Based on the observed 49 short bursts with Swift/X-ray Telescope follow-up observations, we find that three bursts have bright X-ray flares, among which three flares from two bursts are probably related to the central engine reactivity. We argue that these two bursts may originate from the BH-NS merger rather than the NS-NS merger. Our suggested link between the central engine-powered bright X-ray flare and the BH-NS merger event can be checked by the future gravitational wave detections from advanced LIGO and Virgo.