ipolar: emission from the accretion column of a magnetized white dwarf in intermediate polars

The models in the ipolar.fits additive table model file represent hard X-ray emission (3-200 keV) of the post-shock structures (PSR), or accretion columns, of magnetized white dwarfs in intermediate polars.

Accretion discs in this kind of objects are disrupted by the magnetic field of the compact object at the magnetospheric radius. Accreting matter then follows the magnetic field lines and forms a shock above the white dwarf surface. Heated matter cools down radiating the hard X-ray emission and settles onto the white dwarf surface.

The models of PSRs were computed in pseudo-dipole geometry ignoring the cyclotron cooling. The shape of a PSR spectrum depends on the free-fall velocity at the white dwarf surface, which in turn depends on the two parameters, the white dwarf mass and the magnetospheric radius. The well known mass-radius dependence for white dwarfs was used to exclude the white dwarf radius (Nauenberg 1972).

The details are described in the paper Suleimanov et al. 2016, A&A (arXiv:1604.00232). Please, refer to this paper if you use this model.

The model grid is computed for 56 white dwarf masses from 0.3 to 1.4 solar masses with the step 0.02 solar masses.

The second parameter is the relative magnetospheric radius r_m = R_m / R_wd. This parameter is distributed uniformly on the function R_m / R_wd from r_m = 1.5 to r_m = 60, and one additional model with r_m = 1000 was added to mimic the infinite magnetospheric radius. In total the grid is thus computed for 41 relative magnetospheric radii.

Model parameters are:

  • the white dwarf mass in solar masses M_wd / M_sun

  • the relative magnetospheric radius R_m / R_wd

  • the normalization K = f (R_wd / d)^2, where d is the distance in cm, and f is the fraction of the white dwarf surface occupied by the PSR footprint.

The table model file can be downloaded as ipolar.fits and used by e.g. model atable{ipolar.fits}.

Keith Arnaud, Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center

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Last modified: Thursday, 21-Apr-2016 13:14:01 EDT