Diffuse Gamma-rays Produced in Cosmic-ray Interactions and the Tev-band Spec- Trum of Rx J1713.7-3946 the Γ-ray Production Matrix

We employ the Monte Carlo particle collision code DPMJET3.04 to determine the multiplicity spectra of various secondary particles (in addition to π 0 's) with γ's as the final decay state, that are produced in cosmic-ray (p's and α's) interactions with the interstellar medium. We derive an easy-to-use γ-ray production matrix for cosmic rays with energies up to about 10 PeV. This γ-ray production matrix is applied to the GeV excess in diffuse Galactic γ-rays observed by EGRET, and we conclude the non-π 0 decay components are insufficient to explain the GeV excess, although they have contributed a different spectrum from the π 0-decay component. We also test the hypothesis that the TeV-band γ-ray emission of the shell-type SNR RX J1713.7-3946 observed with HESS is caused by hadronic cosmic rays which are accelerated by a cosmic-ray modified shock. By the χ 2 statistics, we find 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 cutoff at 50-100 TeV is imposed on the particle spectrum. It is generally believed that diffuse galactic γ-rays are a good probe of the production sites and also the propagation of accelerated charged particles in the Galactic plane (see [3] and references therein). Exact knowledge of the γ-ray source spectrum resulting from hadronic interactions is of prime importance for a proper physical interpretation for the diffuse γ-rays. The production of neutral pions and their subsequent decay to γ-rays is thought to be the principal mechanism for the γ-ray hadronic component in cosmic ray interactions, and a number of parameterizations have been developed to describe γ-ray production in pp-collision [5, 8]. On the other hand, in addition to the neutral pion production, the direct γ-ray production in cosmic-ray interaction was found important [7], as was the production of (Σ ± , Σ 0), (K ± , K 0), and η particles , all of which eventually decay into γ-rays [8]. Also, the helium nuclei in cosmic rays and the in-terstellar medium are expected to contribute about 20-30% to the secondary production in cosmic-ray interactions, for which the multiplicity spectra may be different. In a hadronic interaction, the multi-plicity of non-π 0 secondaries with γ-rays as the final decay states is about 50% of the π 0 multiplicity. These non-π 0 secondaries in hadronic interactions might present a …