Interstellar Radiation Field

Cosmic rays produce gamma rays through the inverse Compton interaction with photons of the cosmological background and of the interstellar radiation field (ISRF). In order to account for this component we use the analytical model proposed by Cox [Cox et al., 1986], and parametrized by Chi & Wolfendale [Chi & Wolfendale, 1991]. It describes the ISRF as the result of three main contributions: far infrared (due to dust emission), near infrared and optical/UV (due to stars emission). A more detailed model of ISRF has been more recently developed by [Strong et al., 2000], in which the spectrum of each components is derived (see figure 1.6). However we have considered that, for our purposes, the simpler Cox model is sufficient. We let as future improvement of the gamma-ray emissivity model a study of the differences that would imply the use of a more refined ISRF model.