comptt

This is an analytic model describing Comptonization of soft photons in a hot plasma, developed by L. Titarchuk (see ApJ, 434, 313). This replaces the Sunyaev-Titarchuk Comptonization model in the sense that the theory is extended to include relativistic effects. Also, the approximations used in the model work well for both the optically thin and thick regimes. The Comptonized spectrum is determined completely by the plasma temperature and the so-called parameter which is independent of geometry. The optical depth is then determined as a function of for a given geometry. Thus par5 switches between spherical and disk geometries so that is not a direct input here. This parameter MUST be frozen. If , is obtained from the optical depth using analytic approximation (e.g. Titarchuk 1994). If and , is obtained by interpolation from a set of accurately calculated pairs of and from Sunyaev & Titarchuk 1985 (A&A 143, 374). In this incarnation of the model, the soft photon input spectrum is a Wien law [x**2 exp(-x) photons] because this lens itself to a particularly simple analytical form of the model. For present X-ray detectors this should be adequate. Note that in energy flux space the peak of the Wien law occurs at 3kT as opposed to 2.8kT for a blackbody. The spectral fitter is strongly urged to read the following references before using this model in order to fully understand and appreciate the physical assumptions made : Titarchuk, L., 1994, ApJ, 434, 313; Hua, X-M., Titarchuk, L., 1995, ApJ, 449, 188; Titarchuk, L., Lyubarskij, Y., 1995, ApJ, 450, 876.

par1	 = 	 Redshift.

par2	 = 	 Input soft photon (Wien) temperature (keV).

par3	 = 	 Plasma temperature (keV).

par4	 = 	 Plasma optical depth.

par5	 = 	 Geometry switch. ABS(par5) <=1 : disk, >1: sphere.

       	           : use analytic approx for    vs.   .

                   : Get beta vs. tau from interpolation.

K   	 = 	 ?