Linking burst-only X-ray binary sources to faint X-ray transients

TL;DR

This study links burst-only X-ray sources to faint X-ray transients by observing their outbursts and quiescent states, providing insights into their nature as neutron star transients.

Contribution

It presents the first systematic Swift observations of burst-only sources, identifying outbursts and faint counterparts, and discusses their relation to neutron star transients.

Findings

Detected outbursts in some burst-only sources.

Identified faint quiescent counterparts.

Discussed the connection to neutron star transients.

Abstract

Burst-only sources are X-ray sources showing up only during short bursts but with no persistent emission (at least with the monitoring instrument which led to their discovery). These bursts have spectral characteristics consistent with thermonuclear (type I) burst from the neutron star surface, linking burst-only sources to neutron star X-ray binary transients. We have carried out a series of snapshot observations of the entire sample of burst-only sources with the Swift satellite. We found a few sources in outburst and detect faint candidates likely representing their quiescent counterparts. In addition, we observed three quasi-persistent faint X-ray binary transients. Finally we discuss burst-only sources and quasi-persistent sources in the framework of neutron star transients.