White dwarf masses in intermediate polars observed with the Suzaku satellite^*

¹ Department of Physics, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan e-mail: yuasa@juno.phys.s.u-tokyo.ac.jp
² Cosmic Radiation Laboratory, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
³ Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, 3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
⁴ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
⁵ Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan
⁶ Department of Astrophysics, School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan

Received: 30 March 2010
Accepted: 7 June 2010

Abstract

Context. White dwarfs (WDs) in cataclysmic variables (CVs) are important experimental laboratories where the electron degeneracy is taking place on a macroscopic scale. Magnetic CVs increase in number especially in the hard X-ray band (≳ 10 keV) thanks to sensitive hard X-ray missions.

Aims. From X-ray spectroscopy, we estimate the masses of nearby WDs in moderately-magnetized CVs, or Intermediate Polars (IPs).

Methods. Using the Suzaku satellite, we aquired wide-band spectra of 17 IPs, covering 3–50 keV. An accretion column model of Suleimanov et al. (2005, A&A, 435, 191) and an optically-thin thermal emission code were used to construct a spectral emission model of IPs with resolved Fe emission lines. By simultaneously fitting the Fe line complex and the hard X-ray continuum of individual spectra, the shock temperature and the WD mass were determined with a better accuracy than in previous studies.

Results. We determined the WD masses of the 17 IPs with statistical fitting errors of ≲ 0.1–0.2  in many cases. The WD mass of a recently-found IP, IGR J17195-4100, was also estimated for the first time (1.03^+0.24_-0.22 ). The average WD mass of the sample is 0.88±0.25 . When our results were compared with previous X-ray mass determinations, we found significant deviation in a few systems although the reason of this is unclear. The iron abundance of the accreting gas was also estimated, and confirmed the previously reported sub-solar tendency in all sources with better accuracy.