Thermal and bulk Comptonization of a seed blackbody-like spectrum

NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual

This model describes the Comptonization spectrum of soft photons off electrons which are either purely thermal or additionally subjected to an inward bulk motion. It consists of two components: one is the direct seed photon spectrum and the other one is the Comptonizated spectrum. The latter is obtained as a self-consistent convolution of the seed photon spectrum with the system Green's function.

The model is not specific to bulk Comptonization but it includes in a coherent way different spectral shapes such as simple blackbody (i.e. neither thermal nor bulk Comptonization), thermal Comptonization (equivalent to compTT) and thermal plus bulk Comptonization. In the latter case, it can be considered a completion and update of the BMC model, as it includes the cut-off term in the spectrum.

par1 = kTs, temperature of the seed photons (keV)
par2 = gamma, index of the seed photon spectrum (default gamma=3)
par3 = alpha, energy index of the Comptonization spectrum
par4 = delta, bulk parameter, efficiency of bulk over thermal Comptonization
par5 = kTe, temperature of the electrons (keV)
par6 = log(A), log of the illuminating factor parameter (A)
par7 = Cn, normalization of the seed photon spectrum, defined in the same way as the XSPEC bbody model

All mathematical details of the model and its validity limits for applications are reported in Farinelli et al. (2008, ApJ, 680, 602). The source code, model file, and a guide to installing this model are included in this tar file.


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

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