XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8-330920 in the Galactic Disk

Abstract

We aim at characterizing the population of low-luminosity X-ray sources in the Galactic plane by studying their X-ray spectra and periodic signals in the light curves. We are performing an X-ray survey of the Galactic disk using XMM-Newton, and the source XMMU J173029.8-330920 was serendipitously discovered in our campaign. We performed a follow-up observation of the source using our pre-approved NuSTAR target of opportunity time. We used various phenomenological models in xspec for the X-ray spectral modeling. We also computed the Lomb-Scargle periodogram to search for X-ray periodicity. A Monte Carlo method was used to simulate 1000 artificial light curves to estimate the significance of the detected period. We also searched for X-ray, optical, and infrared counterparts of the source in various catalogs. The spectral modeling indicates the presence of an intervening cloud with $N_{\mathrm{H}}\sim (1.5-2.3)\times 10^{23}\mathrm{c}{\mathrm{m}}^{-2}$ that partially absorbs the incoming X-ray photons. The X-ray spectra are best fit by a model representing emission from a collisionally ionized diffuse gas with plasma temperature $kT=26_{-5}^{+11}$ keV. Furthermore, an Fe $K_{\alpha }$ line at $6.47_{-0.06}^{+0.13}$ keV was detected with an equivalent width of the line of $312\pm 104$ eV. We discovered a coherent pulsation with a period of $521.7\pm 0.8$ s. The 3-10 keV pulsed fraction of the source is around $\sim$50-60\%. The hard X-ray emission with plasma temperature $kT=26_{-5}^{+11}$ keV, iron $K_{\alpha }$ emission at 6.4 keV and a periodic behavior of $521.7\pm 0.8$ s suggest XMMU J173029.8-33092 to be an intermediate polar. We estimated the mass of the central white dwarf to be $0.94-1.4M_{\odot }$ by assuming a distance to the source of $\sim 1.4-5$ kpc.

7 pages, 4 figures, accepted for publication in A&A

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