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 \(N_{\rm H}\sim(1.5-2.3)\times10^{23}\ \rm cm^{-2}\) 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 \(kT=26^{+11}_{-5}\) keV. Furthermore, an Fe \(K_{\alpha}\) line at \(6.47^{+0.13}_{-0.06}\) keV was detected with an equivalent width of the line of \(312\pm104\) eV. We discovered a coherent pulsation with a period of \(521.7\pm0.8\) s. The 3-10 keV pulsed fraction of the source is around \(\sim\)50-60\%. The hard X-ray emission with plasma temperature \(kT=26^{+11}_{-5}\) keV, iron \(K_{\alpha}\) emission at 6.4 keV and a periodic behavior of \(521.7\pm0.8\) s suggest XMMU J173029.8-33092 to be an intermediate polar. We estimated the mass of the central white dwarf to be \(0.94-1.4\ M_{\odot}\) by assuming a distance to the source of \(\sim1.4-5\) kpc.