An X-ray and optical study of the ultracompact X-ray binary A1246-58

TL;DR

This study combines X-ray and optical observations to analyze the ultracompact X-ray binary A1246-58, revealing its hydrogen-deficient spectrum, distance, burst characteristics, and variable interstellar medium composition.

Contribution

It provides the first detailed multi-wavelength analysis confirming the ultracompact nature and unique spectral features of A1246-58, including its distance and burst behavior.

Findings

Lack of hydrogen spectral features supports UCXB classification.

Distance of 4.3 kpc determined from X-ray burst spectroscopy.

Detection of intermediately long thermonuclear bursts.

Abstract

Results are discussed of an X-ray and optical observation campaign of the low-mass X-ray binary A1246-58 performed with instruments on Satellite per Astronomia X ('BeppoSAX'), the Rossi X-ray Timing Explorer (RXTE), the X-ray Multi-mirror Mission ('XMM-Newton'), the Swift mission, and the Very Large Telescope. Spectra and flux time histories are studied. The most important results are the lack of hydrogen spectral features in the optical spectrum, supporting the proposition that this is an ultracompact X-ray binary (UCXB), the determination of a 4.3 kpc distance from time-resolved spectroscopy of thermonuclear X-ray bursts, and the detection of intermediately long thermonuclear bursts as seen in a number of other UCXBs. There is evidence for a Ne/O abundance ratio in the line of sight that is higher than solar and variable. This may be due to different changes in the ionization degrees of Ne and O, which may be related to the variable irradiating flux. We discuss the spectral variability and the peculiarities of the long-term light curve.