An intermediate polar candidate toward the Galactic plane

Abstract

Context. For the past decade, it has been suggested that intermediate polars (IPs), a subclass of magnetic cataclysmic variables (CVs), are one of the main contributors to the hard diffuse X-ray emission from the Galactic center (GC) and Galactic ridge. Aims. In our ongoing XMM-Newton survey of the central region of the Galactic disk (20° ×2°), we detected a persistent IP candidate, 1.7° away from the GC. In this work, we better characterize the behavior of this source by looking at the new and archival XMM-Newton data. Methods. We performed a detailed X-ray spectral modeling of the source. Furthermore, we searched for X-ray pulsations in the light curve as well as its counterpart at other wavelengths. Results. The XMM-Newton spectrum (0.8–10 keV) of the source is described by a partial covering collisionally ionized diffuse gas with plasma temperature kT = 15.7−3.6+20.9 keV. In addition, the spectrum shows the presence of iron lines at E = 6.44, 6.65, and 6.92 keV with equivalent widths of 194−70+89, 115−75+79, and 98−74+93 eV, respectively. The X-ray light curve shows a coherent modulation with a period of P = 432.44 ± 0.36 s, which we infer is the spin period of the white dwarf. The white dwarf mass estimated from fitting a physical model to the spectrum results in MWD = 1.05−0.21+0.16 M⊙. We were able to find a likely optical counterpart in the Gaia catalog with a G magnitude of 19.26, and the distance to the source derived from the measured Gaia parallax is ∼4.3 kpc. Conclusions. We provide an improved source localization with subarcsec accuracy. The spectral modeling of the source indicates the presence of intervening circumstellar gas, which absorbs the soft X-ray photons. The measured equivalent width of the iron lines and the detection of the spin period in the light curve are consistent with those from IPs.