Twophase Comptonization model of soft thermal
seed photons for GRB prompt emission.
This GRBCOMP 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 twophase model: up to the peak energy E_{p}
of the EF(E) spectrum soft thermal blackbodylike photons are
comptonized by a subrelativistic bulk outflow of thermal electrons,
while the highenergy 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).
The model parameters are the following:
par1 = kT_{s}, temperature of the seed
blackbody spectrum (keV)
par2 = γ, when it is set = 3 the seed soft spectrum is a blackbody, otherwise it approximates a modified blackbody
par3 = kT_{e}, electron temperature of the
subrelativistic outflow (keV)
par4 = τ, radial optical depth of the subrelativistic
outflow
par5 = β, bulk outflow velocity of the thermal electrons
par6 = fbflag, if set = 0 only the firstorder
bulk Comptonization term is considered, if set =1 also the secondorder term 1+β^{2}/3Θ is computed, where Θ=kT_{e}/m_{e}c^{2}
par7 = log(A), geometrical covering factor which determines the relative weigths of the seed and comptonized spectra to the total flux
par8 = z, redshift
par9 = αboost, energy index of the Green's function with which the formerly comptonization spectrum is convolved
norm = R^{2}_{9}
/D^{2}_{Mpc}, where R_{9} is the apparent
blackbody radius in units of 10^{9} cm and D_{Mpc }is
the sorce distance in Mpc
To install as an XSPEC local model download the source code and model
description file.
Keith Arnaud,
Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center
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