Cyclotron emission from accretion plasma columns in magnetic cataclysmic variable stars

¹ Department of Physics, İzmir Institute of Technology, İzmir 35430, Turkey e-mail: belinda@astronomy.sci.ege.edu.tr
² University of Ege, Faculty of Science, Department of Astronomy and Space Sciences, 35100 Bornova, İzmir, Turkey
³ Katholieke Universiteit Leuven, Instituut voor Sterrenkunde Celestijnenlaan 200B, 3001 Leuven, Belgium

Received: 3 August 2004
Accepted: 15 April 2005

Abstract

Pure cyclotron spectra of polars produced during their low accretion states are deduced. We used the working hypothesis that the cyclotron emission is produced by electrons spiraling down the dipole magnetic field lines and forming an accretion plasma column on top of the magnetic pole of a white dwarf. The velocity distribution function of electrons emitting cyclotron radiation is assumed to be a bi-Maxwellian. Since the radiating electrons in a million–Gauss magnetic field seek their respective magnetic mirrors, the perpendicular components of their velocity vectors are assumed to be greater than the parallel ones in the radiation region. This assumption implies that the cyclotron radiation is emitted more or less in the perpendicular direction (to the local magnetic field). Then we investigated the contribution of the ordinary and the extraordinary wave modes to the luminosity. The model predictions seem to be consistent with observations. We present the model cyclotron spectra of a randomly chosen polar, UZ For, as a case study.