Searching for single-frame rapid X-ray transients detected with Chandra

TL;DR

This paper introduces a new method to detect rapid X-ray transients in Chandra data, discovering 11 events and discussing their possible origins, which could include gamma-ray bursts, neutron stars, and black holes.

Contribution

The paper presents a novel detection technique for rapid X-ray transients using single-frame photon counts, expanding the ability to identify faint and short-lived astrophysical phenomena.

Findings

Discovered 11 rapid X-ray transient events in Chandra archive.

Estimated detection rate of short gamma-ray burst related transients.

Method can potentially reveal quiescent black holes with few photons.

Abstract

We propose a new method to identify rapid X-ray transients observed with focusing telescopes. They could be statistically significant if three or more photons are detected with Chandra in a single CCD frame within a point-spread-function region out of quiescent background. In the Chandra archive, 11 such events are discovered from regions without point-like sources, after discrimination of cosmic rays and background flares and control of false positives. Among them, two are spatially coincident with extended objects in the Milky Way, one with the Small Magellanic Cloud, and another one with M31; the rest have no or a dim optical counterpart ($\gtrsim 20$ mag), and are not clustered on the Galactic plane. Possible physical origins of the rapid transients are discussed, including short gamma-ray bursts (GRBs), short-lived hypermassive neutron stars produced by merger of neutron stars, accreting compact objects in the quiescent state, magnetars, and stellar flares. According to the short GRB event rate density, we expect to have detected $2.3_{-0.6}^{+0.7}$ such events in the Chandra archive. This method would also allow us to reveal quiescent black holes with only a few photons.