XMM-Newton observations of the complex spin pulse of the intermediate polar PQ~Geminorum

Abstract

The intermediate polar PQ Geminorum shows a complex pulsation, caused by a spinning white dwarf, which varies markedly with wavelength. We report XMM-Newton observations, including the soft and hard X-ray bands and the first UV lightcurves of this star. We update the ephemeris for PQ Gem allowing us to align these data with a compilation of lightcurves from the optical to the X-ray. Building on work by previous authors, we show how a model in which accretion flows along skewed field lines, viewed at the correct inclination, can explain the major features of the lightcurves in all bands. We discuss how the skew of the field lines relates to the spinning down of the white-dwarf rotation.