Classifying IGR J20084+3221 as an Intermediate Polar with XMM-Newton and NuSTAR

This paper reports the results of a periodic search and spectral analysis of the X-ray source IGR J20084+3221 in the Milky Way, based on observations from XMM-Newton and NuSTAR. The source was previously considered a high-mass X-ray binary (HMXB) or magnetic cataclysmic variable (MCV). Using the Z₁² test method, we detected significant periodic signals: 636.7 ± 0.9 s from the XMM-Newton data and 635.5 ± 0.4 s from the NuSTAR data, which are consistent within the margin of error. Spectral fitting revealed a plasma temperature of kT = 31 ± 4 keV, along with the detection of Fe Kα fluorescence lines and Fe XXV and Fe XXVI emission lines. The inclusion of a partial covering absorption model significantly improved the spectral fitting. The pulse fraction was observed to decrease with increasing energy. These characteristics are consistent with those of an intermediate polar (IP). Therefore, we identify IGR J20084+3221 as an intermediate polar, with the detected period corresponding to the spin period of the white dwarf. Using multi-temperature X-ray emission model developed for intermediate polars (ipolar.fits), we estimate the mass of the white dwarf to be 1.181± 0.083 M.