An intermediate polar candidate toward the Galactic plane

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
e-mail: samaresh.mondal@inaf.it
² Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
³ Columbia Astrophysics Laboratory, Columbia University, Columbia, NY 10027, USA
⁴ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, E-08193 Barcelona, Spain
⁵ Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capità 2–4, 08034 Barcelona, Spain

Received: 14 June 2022
Accepted: 30 August 2022

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 M_WD = 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.