On the origin of the Fe Kα emission line from intermediate polar EX Hyrae

Abstract

We present spectral analysis of intermediate polar EX Hya observed with Suzaku satellite on 18-07-2007 for 91 kilo seconds (ks). We model the spectrum with an absorbed thermal bremsstrahlung and three Gaussian lines for the Fe Kα line complex. We resolved the 6.4, 6.7, and 7.0 keV lines, each corresponding to the neutral (or low-ionized), He-like, and H-like iron ions. The fluorescence line is due to irradiation of neutral (or low ionized) material (iron) by hard X-ray sources, as a collisional origin would lead to rapid ionization. The He-like and H-like iron ions are emissions created by collisional excitation and photoionization/excitation in the vicinity of the hot white dwarf (WD). We study the emission of these lines in EX Hya and found that the fluorescence line is likely created by reflection of hard X-rays from the N_H absorption columns as our search for the reflection of hard X-rays on the surface of the WD yielded a null result. The 6.7 and 7.0 keV lines, however, are largely emitted through collisional excitation in the vicinity of the compact white dwarf shock heated by the shock front. We also discussed Fe Kα emission line as a diagnostic tool for high energy astrophysical sites.