ROSAT and Ginga observations of the magnetic cataclysmic variable QQ Vul: evidence for two-pole accretion

A. P. Beardmore, G. Ramsay, J. P. Osborne, K. O. Mason, J. A. Nousek, C. Baluta

We report observations made in 1991 April of QQ Vul using the ROSAT and Ginga satellites. We find a spectral variation in soft X-rays that can be accounted for by an increase in the blackbody temperature by 3-5 eV, or by an increase in the intrinsic absorbing column density of $(1.8-3.6)\times10^{19}\text{cm}^{-2}$, between phases 0.5 and 1.0. Together with evidence for separated hard and soft X-ray emission regions, this suggests the presence of two-pole accretion. The emission region furthest from the secondary has a soft X-ray excess ≳2.5, suggesting buried shocks arising from the accretion of dense filaments. The other emission region, closer to the secondary, is the site of the hard X-ray component. The hard X-ray data show a 6.7-keV iron K line of large equivalent width.