Gamma-Rays Produced in Cosmic-Ray Interactions and the TeV-band Spectrum of RX J1713-3946

We study the individual contribution to diffuse $\gamma$-ray emission from the secondary products in hadronic interactions generated by cosmic rays (CRs), in addition to the contribution of $\pi^0$ decay. For that purpose we employ the Monte Carlo particle collision code DPMJET3.04 to determine the multiplicity spectra of various secondary particles with $\gamma$'s as the final decay state, that result from inelastic collisions between cosmic-ray protons and Helium nuclei and the interstellar medium with standard composition. We thus derive an easy-to-use $\gamma$-ray production matrix for cosmic ray with energies up to about 10 PeV. The production matrices are used to interpret the $\gamma$-ray spectra of diffuse galactic emission and supernova remnants (SNR) and also to the GeV excess in diffuse galactic $\gamma$-rays. We also test the hypothesis that the TeV-band $\gamma$-ray emission of the shell-type SNR RX J1713-3946 observed with HESS is caused by shock-accelerated hadronic cosmic rays. Using the $\chi^2$ statistics we find that a continuously softening spectrum is strongly preferred, in contrast to expectations. A hardening spectrum has about 1\% probability to explain the HESS data, but then only if a hard cut-off at 50-100 TeV is imposed on the particle spectrum.