Polarized radiation in magnetic white dwarfs.
Abstract
A model for magnetic white dwarfs is proposed which attributes the partially polarized light to synchrotron radiation. The source of the radiation is relativistic electrons trapped in the magnetosphere of a white dwarf. The white dwarf's magnetic field is assumed to be dipolar. The Stokes parameters for the synchrotron radiation are tabulated as a function of frequency, observer's orientation, and energy and spatial distribution of the relativistic electrons. The results of the synchrotron calculations are applied to the polarization observations of Grw +7008247 and DQ Herculis. This model can account for the major features of the polarized radiation coming from these two magnetic white dwarfs. The calculations predict for Grw +7008247 that the surface magnetic field is B8 < 4 x 106 gauss, that the incident viewing angle is 450 < 0o < 750, and that the electrons are trapped with nearly an isotropic distribution about the white dwarf. For DQ Herculis the surface magnetic field is B8 <% 7 x 106 gauss and the trapped electrons are confined to a disklike region about the white dwarf. For both cases the density of electrons in the magnetosphere falls in the range of 10 < n < 10 cm - with energies of about 4-35 MeV. Subject headings: polarization - stars: magnetic - stars: white dwarfs - synchrotron radiation
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1976
- DOI:
- 10.1086/154786
- Bibcode:
- 1976ApJ...209..868R