BBXRT spectrum of BY Cam
BBXRT spectrum of the magnetic cataclysmic variable star system BY Cam. The model fit shown is for a thermal bremsstrahlung of kT = 30 keV.
The low energy absorption shows an edge near 0.6 keV, which is consistent with neutral or partially ionized oxygen. Such an edge could arise from absorption by partially ionized material, or material with enhanced oxygen abundance relative to carbon and helium. The spectrum below the edge is consistent with absorption by normal neutral material, with no evidence for a soft blackbody component exceeding 10% of the luminosity of the hard X-ray component for a blackbody temperature of 50 eV. The iron K-line energy is consistent with partially ionized iron, with upper limits ~0.1-0.3 from contribution by neutral or hydrogen-like ions. The absence of a neutral iron line is consistent with the lack of a soft blackbody component, and argues against reprocessing of the hard X-rays on the surface of the white dwarf. Possible explanations for this include reprocessing in a hot optically thick layer on the white dwarf (although this is likely to produce a reprocessed continuum which is detectable at some level), and hard X-ray emission which is preferentially directed away from the white dwarf or which is approximately isotropic but occurs several stellar radii away from the white dwarf surface.
Figure from Kallman et al 1993 ApJ 411, 869.
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