Millihertz Quasi-periodic Optical Oscillations in 4U 0614+091

TL;DR

This paper reports the discovery of a low-frequency optical QPO in 4U 0614+091, which may be linked to accretion disk structure and supports its classification as an ultra-compact binary.

Contribution

It presents the first detection of a millihertz optical QPO in 4U 0614+091 and discusses its implications for the system's nature.

Findings

Detected a 1mHz optical QPO with no X-ray counterpart.

Identified a 48-minute modulation consistent with orbital period.

QPO shows phase jumps, indicating non-coherence.

Abstract

We report the discovery of a 1mHz optical quasi-periodic oscillation (QPO) in the candidate ultracompact low-mass X-ray binary 4U 0614+091. The ultra-low frequency QPO has no X-ray counterpart in contemporaneous RXTE/PCA data and is likely a signature of structure in the accretion disk. The QPO can be reasonably fitted with a single sine wave but with a phase jump part way through the observation, indicating that it is not coherent.We also identify a 48 min modulation, approximately consistent with the suggested orbital period of O'Brien (2005) and Shahbaz et al. (2008). If this is indeed orbital, it supports an identification of 4U 0614+091 as an ultra-compact source.