The changing accretion states of the intermediate polar MU Camelopardalis^*

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Postdam, Germany e-mail: [astaude;aschwope]@aip.de

Received: 22 December 2006
Accepted: 22 April 2008

Abstract

Aims. We study the timing and spectral properties of the intermediate polar MU Camelopardalis (1RXS J062518.2+733433) to determine the accretion modes and the accretion geometry from multi-wavelength, multi-epoch observational data.

Methods. Light curves in different observed energy ranges (optical, UV, X-ray) are extracted. The timescales of variability in these light curves are determined using Analysis of Variance. Phase-resolved X-ray spectra are created with respect to the most prominent detected periodicities and each fitted with an identical model, to quantify the differences in the fitted components.

Results. The published tentative value for the spin period is unambiguously identified with the rotation period of the white dwarf. We detect a distinct soft X-ray component that can be reproduced well by a black body. The analysis of data obtained at different epochs demonstrates that the system is changing its accretion geometry from disk-dominated to a combination of disk- plus stream-dominated, accompanied with a significant change in brightness at optical wavelengths.