Eclipse Timings of the Transient Low Mass X-ray Binary EXO0748-676. IV. The Rossi X-Ray Timing Explorer Eclipses

TL;DR

This paper presents a comprehensive database of 443 X-ray eclipse timings of the low mass X-ray binary EXO0748-676 observed by RXTE, revealing four orbital period epochs and short-term variability.

Contribution

It provides an extensive, updated timing database with improved analysis techniques, enabling detailed study of orbital period changes in EXO0748-676.

Findings

Four distinct orbital period epochs identified.

Detection of short-term changes likely due to secondary star variability.

Enhanced eclipse timing analysis methods implemented.

Abstract

We report our complete database of X-ray eclipse timings of the low mass X-ray binary EXO0748-676 observed by the Rossi X-Ray Timing Explorer (RXTE) satellite. As of this writing we have accumulated 443 full X-ray eclipses, 392 of which have been observed with the Proportional Counter Array on RXTE. These include both observations where an eclipse was specifically targeted and those eclipses found in the RXTE data archive. Eclipse cycle count has been maintained since the discovery of the EXO0748-676 system in February 1985. We describe our observing and analysis techniques for each eclipse and describe improvements we have made since the last compilation by Wolff et al. (2002). The principal result of this paper is the database containing the timing results from a seven-parameter fit to the X-ray light curve for each observed eclipse along with the associated errors in the fitted parameters. Based on the standard O-C analysis, EXO0748-676 has undergone four distinct orbital period epochs since its discovery. In addition, EXO0748-676 shows small-scale events in the O-C curve that are likely due to short-lived changes in the secondary star.