4.1.24. Mbb: modified blackbody model

This model describes the spectrum of a black body modified by coherent Compton scattering. This is in several instances a much better description than a simple black body (for example accretion disk spectra of AGN). The physical background is described for example by Rybicki & Lightman (1986), pages 218–219. The formulae that we use here with a derivation are given by Kaastra & Barr (1989). From that work we derive the spectrum (10^{44} photons/s/keV):

N(E) = 1358. \frac{A E^{0.25} }{ e^{E/T} (e^{E/T}-1)}

where E is the photon energy in keV, T the temperature in keV and A the normalisation in units of 10^{26} \mathrm{m}^{0.5}, defined by

A = n_{\mathrm e}^{0.5}O

with n_{\mathrm e} the electron density (units: 10^{20} \mathrm{m}^{-3}) and O the emitting source area (units: 10^{16} m).

The parameters of the model are:

norm : Normalisation A (in units of 10^{26} \mathrm{m}^{0.5}). Default value: 1.
t : The temperature T in keV. Default value: 1 keV.

Recommended citation: Kaastra & Barr (1989) and Rybicki & Lightman (1986).