The high energy galactic survey of INTEGRAL has uncovered more than 400 sources emitting at energy above 20 keV. Among them, most are galactic X-ray binaries containing a neutron star or extragalactic active nuclei. But nearly one fourth of these sources are still unidentified. A recent study (Bonnet-Bidaud et al., A&A 473, 185-189 (2007); arXiv:0706.1433) now confirms that systems containing white dwarfs also contribute significantly to the galactic high energy emission.
The image shows the location of IGR J00234+6141, one of the faintest sources discovered by INTEGRAL with the corresponding mosaic from the ISGRI camera (lower left). A detailed study of the field (lower right) and associated optical photometry and spectroscopy has led to an identification with a cataclysmic variable, a low mass binary system containing a highly magnetized white dwarf, also called 'Intermediate Polars systems' (IPs). The INTEGRAL spectrum is well decribed by a thermal emission at a temperature of 30 keV. Such high temperatures are achieved at the basis of an accretion column above the white dwarf as depicted in the artist's view above.
About 5% of the INTEGRAL sources have already been identified with IPs and IGR00234+6141 shows that more such faint systems probably exist. As the white dwarfs are much more numerous than the neutron stars, it is anticipated that these systems represent a significant fraction of the unresolved high energy background.
Credits: Service d'Astrophysique(SAp), CEA France; artist view: Mark Garlick
Download the picture [PNG format: 1.8 Mb].
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