Discovery of a Compact X-Ray Object with a 614 s Periodicity in the Direction of the Galactic Center

Abstract

We report on analysis of X-ray, optical, and radio observations of the previously overlooked X-ray source 2CXO J174517.0–321356 located just 3.°2 away from the Galactic center. Timing analysis of X-ray observations of the source with XMM-Newton reveals periodic pulsations with periods of 1228 and 614 s, with the latter being tentatively considered fundamental. On the other hand, an observation of the object with NuSTAR reveals a hard thermal-bremsstrahlung spectrum. Inspection of the archival Very Large Telescope image reveals, however, no obvious optical counterpart down to R > 25 mag. Observations made with ATCA showed a possible faint radio counterpart with a positive spectral index (α > 0.51) between 1 and 3 GHz, but follow-up ATCA and Very Large Array observations at frequencies between 4.5–10 GHz and 3–22 GHz, respectively, could not detect it. Given the properties in these three bands, we argue that the most likely origin of the X-ray source is emission from a new intermediate polar close to the Galactic center. Alternatively, and less likely, it is an ultracompact X-ray binary, which is one of the most compact X-ray binaries.