The Optical Gravitational Lensing Experiment. Optical Counterparts to the X-ray Sources in the Galactic Bulge

TL;DR

This study identifies 209 optical counterparts to X-ray sources in the Galactic bulge using long-term OGLE survey data, revealing diverse variability types and providing valuable astrometric and photometric information.

Contribution

It presents a comprehensive catalog of optical counterparts to X-ray sources in the Galactic bulge, including variability classifications and precise astrometry, based on long-term OGLE observations.

Findings

209 variable objects identified as likely X-ray counterparts

19 non-variable stars also likely counterparts due to positional alignment

Diverse variability types observed among the counterparts

Abstract

We present a sample of 209 variable objects - very likely optical counterparts to the X-ray sources detected in the direction of the Galactic center by the Galactic Bulge Survey (GBS) carried out with the Chandra satellite. The variable sources were found in the databases of the OGLE long term survey monitoring regularly the Galactic bulge since 1992. The counterpart candidates were searched based on the X-ray source position in the radius of 3."9. Optical light curves of the candidates comprise a full variety of variability types: spotted stars, pulsating red giants (potentially secondary stars of symbiotic variables), cataclysmic variables, eclipsing binary systems, irregular non-periodic objects including an AGN (GRS 1734-292). Additionally, we find that positions of 19 non-variable stars brighter than 16.5 mag in the OGLE databases are so well aligned with the X-ray positions (<0."75) that these objects are also likely optical counterparts to the GBS X-ray sources. We provide the OGLE astrometric and photometric information for all selected objects and their preliminary classifications. Photometry of the candidates is available from the OGLE Internet archive, http://ogle.astrouw.edu.pl