XMM-Newton observations of the X-ray soft polar QS Telescopii^⋆

¹ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
e-mail: traulsen@astro.physik.uni-goettingen.de
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Max-Planck-Institut für Extraterrestrische Physik, PO Box 1312, 85741 Garching, Germany
⁴ Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA

Received: 17 December 2010
Accepted: 15 March 2011

Abstract

Context. On the basis of XMM-Newton observations, we investigate the energy balance of selected magnetic cataclysmic variables, which have shown an extreme soft-to-hard X-ray flux ratio in the ROSAT All-Sky Survey.

Aims. We intend to establish the X-ray properties of the system components, their flux contributions, and the accretion geometry of the X-ray soft polar QS Tel. In the context of high-resolution X-ray analyses of magnetic cataclysmic variables, this study will contribute to better understanding the accretion processes on magnetic white dwarfs.

Methods. During an intermediate high state of accretion of QS Tel, we have obtained 20 ks of XMM-Newton data, corresponding to more than two orbital periods, accompanied by simultaneous optical photometry and phase-resolved spectroscopy. We analyze the multi-wavelength spectra and light curves and compare them to former high- and low-state observations.

Results. Soft emission at energies below 2 keV dominates the X-ray light curves. The complex double-peaked maxima are disrupted by a sharp dip in the very soft energy range (0.1−0.5   keV), where the count rate abruptly drops to zero. The EPIC spectra are described by a minimally absorbed black body at 20 eV and two partially absorbed mekal plasma models with temperatures around 0.2 and 3 keV. The black-body-like component arises from one mainly active, soft X-ray bright accretion region nearly facing the mass donor. Parts of the plasma emission might be attributed to the second, virtually inactive pole. High soft-to-hard X-ray flux ratios and hardness ratios demonstrate that the high-energy emission of QS Tel is substantially dominated by its X-ray soft component.