grbcomp: Comptonization for GRB prompt emission

This model has been proposed by Titarchuk et al., 2012, ApJ, 752, 116 as a possible scenario for the spectral emission of the prompt phase of Gamma Ray Bursts.

It is essentially a two-phase model: up to the peak energy E$_{\rm p}$ of the EF(E) spectrum soft thermal blackbody-like photons are comptonized by a subrelativistic bulk outflow of thermal electrons, while the high-energy tail is obtained by a further convolution of the formerly comptonized spectrum with a Green's function. An example of the application of the model to a sample of GRBs can be found in Frontera et al., 2013, ApJ, 779, 175.

par1 = kTs, temperature of the seed blackbody spectrum (keV)
par2 = gamma, when it is set = 3 the seed soft spectrum is a blackbody, otherwise it approximates a modified blackbody
par3 = kTe, electron temperature of the subrelativistic outflow (keV)
par4 = tau, radial optical depth of the subrelativistic outflow
par5 = beta, bulk outflow velocity of the thermal electrons
par6 = fbflag, if set = 0 only the first-order bulk Comptonization term is considered, if set = 1 also the second-order term $1+2\beta/3\Theta$ is computed, where $\Theta=kT_e/m_ec^2$
par7 = log(A), geometrical covering factor which determines the relative weights of the seed and comptonized spectra to the total flux
par8 = z, redshift
par9 = a_boost, energy index of the Green's function with which the formerly comptonization spectrum is convolved
norm = $R^2_9 /D^2_{\rm Mpc}$, where $R_9$ is the apparent blackbody radius in units of $10^9$ cm and $D_{\rm Mpc}$ is the sorce distance in Mpc