The First High-Contrast Images of X-Ray Binaries: Detection of Candidate Companions in the $\gamma$ Cas Analog RX J1744.7$-$2713

TL;DR

This paper presents the first high-contrast images of X-ray binaries, revealing candidate companions and suggesting potential for new insights into stellar environments and formation processes in extreme conditions.

Contribution

It provides the first high-contrast adaptive optics images of X-ray binaries, identifying potential bound companions at wide orbits around RX J1744.7-2713.

Findings

Detected 21 candidate sources near RX J1744.7-2713

Three sources have high probability of being gravitationally bound

Potential to understand stellar multiplicity and formation in extreme environments

Abstract

X-ray binaries provide exceptional laboratories for understanding the physics of matter under the most extreme conditions. Until recently, there were few, if any, observational constraints on the circumbinary environments of X-ray binaries at $\sim$ 100-5000 AU scales; it remains unclear how the accretion onto the compact objects or the explosions giving rise to the compact objects interact with their immediate surroundings. Here, we present the first high-contrast adaptive optics images of X-ray binaries. These observations target all X-ray binaries within $\sim$ 3 kpc accessible with the Keck/NIRC2 vortex coronagraph. This paper focuses on one of the first key results from this campaign: our images reveal the presence of 21 sources potentially associated with the $\gamma$ Cassiopeiae analog high-mass X-ray binary RX J1744.7$-$2713. By conducting different analyses - a preliminary proper motion analysis, a color-magnitude diagram and a probability of chance alignment calculation - we found that three of these 21 sources have a high probability of being bound to the system. If confirmed, they would be in wide orbits ($\sim$ 450 AU to 2500 AU). While follow-up astrometric observations will be needed in $\sim$ 5-10 years to confirm further the bound nature of these detections, these discoveries emphasize that such observations may provide a major breakthrough in the field. In fact, they would be useful not only for our understanding of stellar multiplicity but also for our understanding of how planets, brown dwarfs and stars can form even in the most extreme environments.