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.
Highlights
QS Tel belongs to the group of AM Her-type cataclysmic variables, in which the field strength of the white-dwarf primary is high enough to prevent the formation of an accretion disk
All-Sky Survey (Voges et al 1999; Schwope et al 1995). This means that QS Tel was in an intermediate high state of accretion at the epoch of our observations
QS Tel was in an intermediate high state of accretion during the XMM-Newton observation
Summary
QS Tel belongs to the group of AM Her-type cataclysmic variables, in which the field strength of the white-dwarf primary is high enough to prevent the formation of an accretion disk. It has been discovered in the ROSAT All-Sky Survey, independently in the soft X-ray regime by Beuermann & Thomas (1993) and in the EUV by Buckley et al (1993). We are obtaining XMM-Newton data of soft X-ray selected polars which have not been subject to high-resolution X-ray observations before, and investigate the system properties and a potential dominance of the soft over the hard X-ray flux
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