Photoionized Features in the X-ray Spectrum of EX Hydrae

• Published in: The Astrophysical journal Vol. 711; no. 2
• Main Authors: Luna, G M, Raymond, J C, Brickhouse, N S, Mauche, C W, Proga, D, Steeghs, D, Hoogerwerf, R
• Format: Journal Article
• Language: English
• Published: United States 28.09.2009
• Subjects: GENERAL AND MISCELLANEOUS; PHOTOIONIZATION; RADIATION SOURCES; RADIATIONS; SPIN
• ISSN: 0004-637X; 1538-4357

We present the first results from a long (496 ks) Chandra High Energy Transmission Grating observation of the intermediate polar EX Hydrae. In addition to the narrow emission lines from the cooling post-shock gas, for the first time we have detected a broad component in some of the X-ray emission lines, namely O VIII {lambda}18.97, Mg XII {lambda}8.42, Si XIV {lambda}6.18, and Fe XVII {lambda}16.78. The broad and narrow components have widths of {approx} 1600 km s{sup -1} and {approx} 150 km s{sup -1}, respectively. We also find that the flux of the broad component is modulated at the white dwarf spin period, constraining the region where the gas is formed. We propose a scenario where the broad component is formed in the pre-shock flow photoionized by radiation from the post-shock flow. Because the photoionized region has to be close to the radiation source in order to produce strong photoionized emission lines from ions like O VIII, Mg XII, and Si XIV, our photoionization model constrains the height of the standing shock above the white dwarf surface.