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28 - X-ray polarization from accreting white dwarfs and associated systems

from Part II - Polarized emission in X-ray sources

Published online by Cambridge University Press:  06 July 2010

K. Wu
Affiliation:
University College London
A. McNamara
Affiliation:
University of Sydney
Z. Kuncic
Affiliation:
University of Sydney
Ronaldo Bellazzini
Affiliation:
Istituto Nazionale di Fisica Nucleare (INFN), Rome
Enrico Costa
Affiliation:
Istituto Astrofisica Spaziale, Rome
Giorgio Matt
Affiliation:
Università degli Studi Roma Tre
Gianpiero Tagliaferri
Affiliation:
Osservatorio Astronomico di Brera
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Summary

We present our results of Monte-Carlo simulations of polarized Compton X-rays from magnetic cataclysmic variables, with realistic density, temperature and velocity structures in the accretion flow. Our study has shown that the X-ray linear polarization may reach about 8% for systems with high accretion rates viewed at a high viewing inclination angle. This value is roughly twice the maximum value obtained by previous studies which assumed a cold, static emission region with a uniform density. We also investigate the X-ray polarization properties of ultra-compact double-degenerate binaries for the unipolar-inductor and direct-impact accretor models. Our study has shown negligible X-ray polarization for the unipolar-induction model. However, the direct-impact accretor model may give X-ray polarization levels similar to that predicted for the magnetic cataclysmic variables.

Introduction

Magnetic cataclysmic variables (mCVs) and Ultra-compact double degenerate binaries (UCDs) are potential X-ray polarization sources. The mCVs contain a magnetic white dwarf accreting material from a low-mass, Roche-lobe filling companion star. There are two major types: (i) the AM Herculis binaries (AM Hers, also known as polars) and (ii) the intermediate polars (IPs) (see). In AM Hers, the white-dwarf magnetic field (B ∼ 107 −108 G) is strong enough to lock the whole system into synchronous rotation. It also prohibits the formation of an accretion disk, and the accretion flow is channelled by the magnetic field into the magnetic polar regions of the white dwarf.

Type
Chapter
Information
X-ray Polarimetry
A New Window in Astrophysics
, pp. 187 - 194
Publisher: Cambridge University Press
Print publication year: 2010

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