Discovery of A Compact X-ray Object with A 614s 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$-$321356 located just 3.2$^{\circ}$ away from the Galactic center. Timing analysis of X-ray observations of the source with \textit{XMM-Newton} reveals periodic pulsations with periods of 1228\,s and 614\,s, with the latter being tentatively considered fundamental. On the other hand, an observation of the object with \textit{NuSTAR} reveals hard thermal-bremsstrahlung spectrum. Inspection of the archival VLT image reveals, however, no obvious optical counterpart down to $\rm{R}>25\,$mag. Observations made with ATCA showed a possible faint radio counterpart with a positive spectral index ($\alpha > 0.51$) between 1--3\,GHz, but follow-up ATCA and VLA 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 ultra-compact X-ray binary, which is one of the most compact X-ray binaries.