We report on the discovery of a hydrogen-deficient compact binary (CXOGBS J175107.6- 294037) belonging to the AM CVn class in the Galactic Bulge Survey. Deep archival X-ray observations constrain the X-ray positional uncertainty of the source to 0.57 arcsec, and allow us to uniquely identify the optical and UV counterpart. Optical spectroscopic observations reveal the presence of broad, shallow He I absorption lines while no sign of hydrogen is present, consistent with a high state system. We present the optical light curve from Optical Gravitational Lensing Experiment monitoring, spanning 15 yr. It shows no evidence for outbursts; variability is present at the 0.2 mag level on time-scales ranging from hours to weeks. A modulation on a time-scale of years is also observed. A Lomb-Scargle analysis of the optical light curves shows two significant periodicities at 22.90 and 23.22 min. Although the physical interpretation is uncertain, such time-scales are in line with expectations for the orbital and superhump periods. We estimate the distance to the source to be between 0.5 and 1.1 kpc. Spectroscopic follow-up observations are required to establish the orbital period, and to determine whether this source can serve as a verification binary for the eLISA gravitational wave mission.
Publication Source (Journal or Book title)
Monthly Notices of the Royal Astronomical Society: Letters
Wevers, T., Torres, M., Jonker, P., Wetuski, J., Nelemans, G., Steeghs, D., Maccarone, T., Heinke, C., Hynes, R., Udalski, A., Kostrzewa-Rutkowska, Z., Groot, P., Gazer, R., Szymański, M., Britt, C., Wyrzykowski, L., & Poleski, R. (2016). Discovery of a high state AM CVn binary in the Galactic Bulge Survey. Monthly Notices of the Royal Astronomical Society: Letters, 462 (1), L106-L110. https://doi.org/10.1093/mnrasl/slw141