X-ray polarization properties of the accretion column in magnetic CVs

Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: matt@fis.uniroma3.it

Received: 10 November 2003
Accepted: 26 April 2004

Abstract

The accretion column in magnetic Cataclysmic Variables may have a non negligible Thomson optical depth. A fraction of the thermal radiation from the post-shock region may therefore be scattered – and then polarized – before escaping the column. Moreover, part of the thermal radiation is reflected – and again polarized – by the White Dwarf surface. We show that X-ray polarimetry can provide valuable and probably unique information on the geometry and physical parameters of the accretion column by calculating, by means of Monte Carlo simulations, the expected polarization properties of magnetic CVs as a function of the geometrical parameters (assuming a cylindrical geometry) and the Thomson optical depth of the column. We find that degrees of polarization as high as about 4% can be present, and apply our calculations to the archetypal magnetic CV, AM Herculis.