grbm: gamma-ray burst continuum

A model for gamma-ray burst continuum spectra developed by Band et al. (1993).

$$A(E)= \left\{ \begin{array}{ll} K(E/100.)^{\alpha_1} \exp(-... ...x{if $E > E_c(\alpha_1 - \alpha_2)$} \\ \end{array} \right.$$

where $E$ is in units of keV and the parameters are:

par1	$\alpha_1$, first power law index
par2	$\alpha_2$, second power law index
par3	$E_c$, characteristic energy in keV
norm	$K$, normalization constant