An intermediate polar candidate toward the Galactic plane

Abstract

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. In our ongoing \emph{XMM-Newton} survey of the central region of the Galactic disk ($20^{\circ }\times 2^{\circ }$), we detected a persistent IP candidate, $1.7^{\circ }$ 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. 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. 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 $P=432.44\pm 0.36$ 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 $M_{\mathrm{WD}}=1.05_{-0.21}^{+0.16}{M}_{\odot }$. 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 $\sim$4.3 kpc. 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.

arXiv comment6 pages, 5 figures, accepted for publication in A&A

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Cited by in corpus (3)

• Discovery of periodicities in two highly variable intermediate polars towards the Galactic Center
• Periodicity from X-ray sources within the inner Galactic disk
• XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8-330920 in the Galactic Disk