Decade time-scale modulation of low mass X-ray binaries

TL;DR

This study analyzes over ten years of X-ray data from low mass X-ray binaries, revealing potential decade-scale sinusoidal flux variations in half of the brightest systems, suggesting long-term modulation mechanisms.

Contribution

It presents the first evidence of decade-scale modulation in low mass X-ray binaries using long-term observational data.

Findings

Up to eight of sixteen bright systems show decade-scale sinusoidal variations.

Possible origins include a third object or intrinsic donor star variability.

Long-term modulations may be more common than previously thought.

Abstract

Regular observations by the All Sky Monitor aboard the Rossi X-ray Timing Explorer satellite have yielded well-sampled light-curves with a time baseline of over ten years. We find that up to eight of the sixteen brightest persistent low mass X-ray binaries show significant, possible sinusoidal, variations with periods of order ten years. We speculate on its possible origin and prevalence in the population of low mass X-ray binaries and we find the presence of a third object in the system, or long-period variability intrinsic to the donor star, as being attractive origins for the X-ray flux modulation we detect. For some of the objects in which we do not detect a signal, there is substantial short-term variation which may hide modest modulation on long time-scales. Decade time-scale modulations may thus be even more common.