Spectrum of a relativistic accretion disk around a spinning black hole
BHSPEC is a spectral fitting model which has been implemented as a additive table model for the Xspec Spectral Fitting Package. It consists of a large grid of tabulated artificial spectra which are used to fit data via interpolation. Currently, the model is comprised of multiple files which cover different, but overlapping, regions of parameter space.
Our method for generating the artificial spectra is described in detail in Davis et al. (2005, ApJ, 621, 372) and Davis & Hubeny (submitted to ApJ). The spectra are based on fully relativistic accretion disk models similar to the KERRBB model already implemented in Xspec. The main difference between KERRBB and BHSPEC is the treatment of the emission at disk surface. KERRBB utilizes a color-corrected blackbody prescription with either isotropic emission or an analytic limb darkening profile. BHSPEC uses stellar atmospheres-like calculations of disk annuli to self-consistently calculate the vertical structure and radiative transfer. The spectra from these calculations are tabulated in the parameters of interest and then used to calculate the spectra at a given radius via interpolation.
The BHSPEC model is parameterized as follows: (note that parameters and their ordering may vary slightly from file-to-file)
The table model files available are bhspec.fits.gz and bhspec2.fits.gz. The first file considers black hole spins (a/M) extending from 0 - 0.8 for alpha=0.1 and 0.01 (alpha is the standard 'anomalous viscocity' parameter). The other file covers a larger range of spin (a/M from 0 - 0.99), but only for alpha=0.01. This partitioning is needed because the disk annuli of high spin, low alpha models do not converge.
Keith Arnaud, Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center
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