======================== GGRB spectral model ======================== This package contains the GGRB spectral model suitable to be used in XSPEC (see http://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/XSappendixLocal.html) This model has been used to perform the gamma-ray burst spectral analysis on Fermi/GBM data discussed in MNRAS, 448, 403C, 2015: "There is a short gamma-ray burst prompt phase at the beginning of each long one" Authors: Calderone, G.; Ghirlanda, G.; Ghisellini, G.; Bernardini, M. G.; Campana, S.; Covino, S.; D'Avanzo, D'Elia, V.; Melandri, A.; Salvaterra, R.; Sbarufatti, B.; Tagliaferri, G. ADS: http://adsabs.harvard.edu/abs/2015MNRAS.448..403C *** INTRODUCTION The GGRB can be used as a spectral model to fit Gamma-Ray Burst (GRB) spectra. It is designed to replace both the cutoff power law (CUTOFFPL) and the Band (GRBM, Band et al., 1993, ApJ, 413, 281) spectral models. The main advantages of the GGRB model are: - it uses an integrated flux (in an energy band defined by the user) as a free parameter in the fit, while both the CUTOFFPL and GRBM models use a model normalization at a given energy. This is very useful when we are interested in the integrated flux in a given band, since we do not have to propagate the parameter uncertainties through the parameter covariance matrix. A possible alternative would be to use the CFLUX convolution model (already available in XSPEC), although it requires the integration energy range to lie within the band defined in the detector response matrix. GGRB provides a greatest flexibility since it relaxes this requirement; - both the peak energy and the integrated flux are parametrized ith logarithmic quantities (log_Ep and log_Flux). This results in simpler and more symmetric parameter uncertainties, with respect to their linear counterparts (see Cabrera et al., 2007, MNRAS, 382, 342); *** MODEL PARAMETERS The GGRB model has eight parameters: 1 - alpha: the photon spectral index for energies smaller than the peak energy; 2 - beta: the photon spectral index for energies greater than the peak energy; (only for the Band model); 3 - log_Ep: the logarithm of the energy of the spectrum peak in the nuFnu representation [keV]; 4 - log_Flux: the logarithm of the integrated flux (in units of erg s^-1 cm^-2) in the energy band defined by Emin and Emax; 5 - Emin: lower limit of the integration energy band [keV]; 6 - Emax: higher limit of the integration energy band [keV]; 7 - opt: option setting to select the spectral model: - 0: cutoff power law - 1: Band model 8 - norm: overall model normalization *** USAGE The GGRB model is an XSPEC additive model designed to replace the CUTOFFPL and GRBM spectral models in GRB spectral fitting. The opt parameter is used to select the appropriate spectral model: either the cutoff power law (opt=0) or the Band model (opt=1). The opt parameter must be freezed for fitting. The alpha parameter is either the photon spectral index of the cutoff powerlaw or the low-energy photon spectral index of the Band model. The beta parameter is the high-energy photon spectral index of the Band model. When the cutoff power law model is selected (opt=0) the beta parameter must be freezed for fitting. The log_Ep parameter is the logarithm (base 10) of the energy of the spectrum peak in the nuFnu representation. Note however that the spectrum will have a peak only if alpha>-2 and alpha>beta. The log_Flux parameter is the logarithm (base 10) of the integrated flux in the energy band defined by Emin and Emax. The Emin and Emax parameters must be freezed for fitting. The norm parameter must be set to 1 and freezed during fitting, since the model normalization is provided by the log_Flux parameter. An example of the usage of the GGRB model is given in the test_ggrb.xcm file. *** INSTALL In order to install the model to a local directory (say ~/xspec_models) on a UNIX-like platform run these commands: rm -rf ~/xspec_models/ggrb mkdir -p ~/xspec_models/ggrb cp ggrb.dat ggrb.cxx ~/xspec_models/ggrb echo "initpackage pkg_ggrb ggrb.dat $HOME/xspec_models/ggrb" | xspec To automatically load the GGRB package each time you start XSPEC add the following line to your XSPEC configuration file (typically ~/.xspec/xspec.rc) lmod pkg_ggrb $HOME/xspec_models/ggrb *** LICENSE Copyright 2014-2015 Giorgio Calderone (giorgio.calderone@gmail.com) XSPEC_GGRB is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. XSPEC_GGRB is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.