Discovery of an Outbursting 12.8 Minute Ultracompact X-Ray Binary

TL;DR

This paper reports the discovery of OGLE-UCXB-01, an ultracompact X-ray binary with a 12.8-minute period, characterized by frequent brightenings, blue color, and X-ray emissions, making it a promising gravitational-wave source.

Contribution

The discovery of a new ultracompact X-ray binary with an extremely short orbital period and unique observational features in a globular cluster.

Findings

12.8-minute orbital period confirmed

Frequent short brightenings observed

Potential gravitational-wave source identified

Abstract

We report the discovery of OGLE-UCXB-01, a 12.8 minute variable object located in the central field of Galactic bulge globular cluster Djorg 2. The presence of frequent, short-duration brightenings at such an ultrashort period in long-term OGLE photometry together with the blue color of the object in Hubble Space Telescope images and the detection of moderately hard X-rays by Chandra observatory point to an ultracompact X-ray binary system. The observed fast period decrease makes the system a particularly interesting target for gravitational-wave detectors such as the planned Laser Interferometer Space Antenna.