4.1.26. 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).