PHOTOIONIZED FEATURES IN THE X-RAY SPECTRUM OF EX HYDRAE

Abstract

We present the first results from a long (496 ks) Chandra High Energy\nTransmission Grating observation of the intermediate polar EX Hydrae. In\naddition to the narrow emission lines from the cooling post-shock gas, for the\nfirst time we have detected a broad component in some of the X-ray emission\nlines, namely O VIII 18.97, Mg XII 8.42, Si XIV 6.18, and Fe XVII 16.78. The\nbroad and narrow components have widths of ~ 1600 km s^-1 and ~ 150 km s^-1,\nrespectively. We propose a scenario where the broad component is formed in the\npre-shock accretion flow, photoionized by radiation from the post-shock flow.\nBecause the photoionized region has to be close to the radiation source in\norder to produce strong photoionized emission lines from ions like O VIII, Fe\nXVII, Mg XII, and Si XIV, our photoionization model constrains the height of\nthe standing shock above the white dwarf surface. Thus, the X-ray spectrum from\nEX Hya manifests features of both magnetic and non-magnetic cataclysmic\nvariables.\n