INTEGRAL/IBIS and Swift/XRT observations of hard cataclysmic variables

Landi, R., Bassani, L., Dean, A.J., Bird, A.J., Fiocchi, M., Bazzano, A., Nousek, J.A. and Osborne, J.P. (2009) INTEGRAL/IBIS and Swift/XRT observations of hard cataclysmic variables. Monthly Notices of the Royal Astronomical Society, 392 (2), 630-640. (doi:10.1111/j.1365-2966.2008.14086.x).

Abstract

The analysis of the third INTEGRAL/Imager on Board Integral Satellite (IBIS) survey has revealed several new cataclysmic variables, most of which turned out to be intermediate polars, thus confirming that these objects are strong emitters in hard X-rays. Here, we present high-energy spectra of all 22 cataclysmic variables detected in the third IBIS survey and provide the first average spectrum over the 20–100 keV band for this class. Our analysis indicates that the best-fitting model is a thermal bremsstrahlung with an average temperature of ?kT?? 22 keV . Recently, 11 (10 intermediate polars and one polar) of these systems have been followed up by Swift/X-ray telescope (XRT) (operating in the 0.3–10 keV energy band), thus allowing us to investigate their spectral behaviour over the range ?0.3–100 keV. Thanks to this wide energy coverage, it was possible for these sources to simultaneously measure the soft and hard components and estimate their temperatures. The soft emission, thought to originate in the irradiated poles of the white dwarf atmosphere, is well described by a blackbody model with temperatures in the range ?60–120 eV. The hard emission, which is supposed to be originated from optically thin plasma in the post-shock region above the magnetic poles, is indeed well modelled with a bremsstrahlung model with temperatures in the range ?16–35 keV, similar to the values obtained from the INTEGRAL data alone. In several cases, we also find the presence of a complex absorber: one totally [with NH? (0.4– 28) × 1021 cm?2 ] and one partially [with NH? (0.7–9) × 1023 cm?2 ] covering the source. Only in four cases (V709 Cas, GK Per, IGR J06253+7334 and IGR J17303?0601), we find evidence for the presence of an iron line at 6.4 keV. We discuss our findings in the light of the systems parameters and cataclysmic variables/intermediate polars modelling scenario.

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Contributors

Author: A.J. Bird

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