Intermediate long X-ray bursts from the ultra-compact binary source SLX 1737-282

TL;DR

This study analyzes intermediate long X-ray bursts from the ultra-compact binary SLX 1737-282, revealing helium ignition processes, burst properties, and source distance, contributing to understanding of nuclear burning in such systems.

Contribution

It provides detailed analysis of two intermediate long bursts from SLX 1737-282, establishing constraints on burst mechanisms and the nature of the accreted material, which was previously not well understood.

Findings

Persistent emission is less than 1% of Eddington luminosity.

Source distance estimated at 7.3 kpc from photospheric radius expansion.

Bursts are consistent with helium ignition at a specific column depth.

Abstract

Aims: The low persistent X-ray burster source SLX 1737-282 is classified as an ultra-compact binary candidate. We compare the data on SLX 1737-282 with the other similar objects and attempt to derive constraints on the physical processes responsible for the formation of intermediate long bursts. Methods: Up to now only three intermediate long bursts, all with duration between ~15-30 minutes, have been recorded for SLX 1737-282. The properties of two intermediate long X-ray bursts observed by INTEGRAL from SLX 1737-282 are investigated. The broadband spectrum of the persistent emission in the 3-100 keV energy band is studied with the INTEGRAL data. Results: The persistent emission is measured to be < 1% Eddington luminosity. From the photospheric radius expansion observed during the bursts we derive the source distance at 7.3 kpc. The observed intermediate long burst properties from SLX 1737-282 are consistent with helium ignition at the column depth of 7-8 x 10E-9 g cm-2 and a burst energy release of 1E41 erg. The apparent recurrence time of ~80 days between the intermediate long bursts from SLX 1737-282 suggests a regime of unstable burning of a thick, pure helium layer slowly accreted from a helium donor star.