Intermediate polars in the Swift/BAT survey: spectra and white dwarf masses

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany e-mail: jcg@mpe.mpg.de
² Dept. of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK e-mail: julo@star.le.ac.uk

Received: 3 November 2008
Accepted: 27 December 2008

Abstract

Context. White dwarf masses in cataclysmic variables are difficult to determine accurately, but are fundamental for understanding binary system parameters, as well as binary evolution.

Aims. We investigate the X-ray spectral properties of a sample of Intermediate Polars (IP) detected above 15 keV to derive the masses of their accreting white dwarfs.

Methods. We use data from the Swift/BAT instrument which during the first 2.5 yrs of operation has detected 22 known intermediate polars. The X-ray spectra of these sources are used to estimate the mass of the white dwarfs.

Results. We are able to produce a mass estimate for 22 out of 29 of the confirmed intermediate polars. Comparison with previous mass measurements shows good agreement. For GK Per, we were able to detect spectral changes due to the changes in the accretion rate.

Conclusions. The Swift/BAT detector with its combination of sensitivity and all-sky coverage provides an ideal tool to determine accurate white dwarf masses in intermediate polars. This method should be applied to other magnetic white dwarf binaries.