Light Curve Morphology Study of UW CrB -- Evidence for a 5 d Superorbital Period

TL;DR

This study analyzes optical light curves of UW CrB, revealing evolving shapes modulated by a 5-day period, likely due to disc precession or warping, and reports 11 new optical bursts supporting an asymmetric accretion disc model.

Contribution

It provides the first evidence of a 5-day superorbital period in UW CrB and documents the evolving morphology of its optical light curves.

Findings

Evidence for a 5-day superorbital period.

Detection of 11 new optical bursts.

Observation of evolving light curve shapes.

Abstract

Since its discovery in 1990, UW CrB (also known as MS1603+2600) has remained a peculiar source without firm classification. Our current understanding is that it is an Accretion Disc Corona (ADC) low mass X-ray binary. In this paper we present results from our photometric campaign dedicated to studying the changing morphology of the optical light curves. We find that the optical light curves show remarkable evidence for strongly evolving light curve shapes. In addition we find that these changes show a modulation at a period of $\sim$ 5 days. We interpret these changes as either due to strong periodic accretion disc warping or other geometrical changes due to disc precession at a period of 5 days. Finally, we have detected 11 new optical bursts, the phase distribution of which supports the idea of a vertically extended asymmetric accretion disc.