Broad-band properties of the hard X-ray cataclysmic variables IGR J00234+6141 and 1RXS J213344.1+510725

Abstract

Context: A significant number of cataclysmic variables have been detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type.
Aims: We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class.
Methods: Timing and spectral analysis of IGR J00234+6141 are based on an XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725, we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data.
Results: We determine a spin period of 561.64 ± 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to ∼2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 ± 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of ∼50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of ∼100 eV. This adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars.
Conclusions: Though showing similar rotational periods and being hard X-ray sources, these two intermediate polars appear different in several respects, among which the presence of a soft X-ray component in 1RXS J213344.1+510725. This source also emits circularly polarized light in the optical band, thus joining the group of soft and polarized intermediate polars as a fifth member. How the hard X-ray and polarized emission are thermalized in these systems is a timely question.

Based on observations obtained with XMM-Newton and INTEGRAL, ESA science missions with instruments and contributions directly funded by ESA Member States and NASA, and with Suzaku, a Japan's mission developed at the Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency in collaboration with US (NASA/GSFC, MIT) and Japanese institutions.