Detailed EXOSAT and optical observations of the intermediate polar 3A0729+103 : discovery of two medium energy X-ray emission regions.

Abstract

EXOSAT observations of the intermediate polar cataclysmic variable 3A0729+103 reveal a strong orbital modulation, with the 2 - 4 keV X-rays being significantly more modulated than the 4 - 6 keV X-rays, indicative of photoelectric absorption. Contemporaneous optical spectroscopy shows that the X-ray minimum occurs at maximum velocity of recession of the Balmer lines and near-maximum equivalent width of the He I 4471 absorption line. The 913 second modulation which is very prominent in the optical light curve, is weakly detected in the medium-energy X-ray light curve, confirming that it represents the white dwarf spin period. These observations are well explained by a combination of two sources of medium-energy X-ray emission; one from the white dwarf magnetic pole(s) and the other from the region where the accretion stream hits the white dwarf magnetosphere. The presence of two emission regions is also clearly seen in the optical spectroscopy.