Orbital-phase-resolved Spectroscopy of the Intermediate Polar FO Aqr Using XMM-Newton Observatory Data

We present the orbital-phase-resolved analysis of an archival FO Aqr observation obtained using the X-ray Multi-Mirror Mission, European Photon Imaging Camera (pn instrument). We investigate the variation of the spin pulse amplitudes over the orbital period in order to account for the effects of orbital motion on spin modulation. The semi-amplitude variations are in phase with the orbital modulation, changing from (38.0 ± 1.8)% at the orbital maximum to (13.3 ± 3.7)% at the orbital minimum. The spectral parameters also show changes over the orbital period. One of the absorption components increase by a factor of five between the orbital minimum and maximum. We interpret that this absorption arises from the bulge where accretion stream from the secondary impacts the disk. The spectrum extracted from the orbital minima and maxima can be fitted with a warm absorber model yielding values N _H = 2.09^+0.98 _-1.09 × 10²² and 0.56^+0.26 _-0.15 × 10²² cm^-2 and log(ξ) = 0.23^+0.37 _-0.26 and <0.30 erg cm s^-1, respectively, indicating the existence of ionized absorption from the bulge at the impact zone which is spread out on the disk. The absorption due to accretion curtain and/or column which causes the spin modulation can be distinguished from the disk absorption via spectral modeling.