The Contribution of Different Supernova Populations to the Galactic Gamma‐Ray Background

The contribution of Source Cosmic Rays (SCRs), accelerated and still confinedin Supernova Remnants (SNRs), to the diffuse high energy \gr emission above 1GeV from the Galactic disk is studied. The \grs produced by the SCRs have amuch harder spectrum than those generated by the Galactic Cosmic Rays (GCRs).Extending a previous paper, a simple SNR population synthesis is considered andthe Inverse Compton emission from the SCR electrons is evaluated in greaterdetail. Then the combined spectrum of \gr emission from the Galactic SupernovaRemnant population is calculated and this emission at low Galactic latitudes iscompared with the diffuse \gr emission observed by the EGRET and ground basedinstruments. The average contribution of SCRs is comparable to the GCRcontribution already at GeV energies, due to Supernovae of types II and Ibexploding into the wind bubbles of quite massive progenitor stars, and becomesdominant at \gr energies above 100 GeV. At TeV energies the dominantcontribution is from SCRs in SNRs that expand into a uniform interstellarmedium. In fact, the sum of hadronic and Inverse Compton \grs would exceed thelimits given by the existing experimental data, unless the confinement time$T_{SN}$, i.e. the time until which SNRs confine the main fraction ofaccelerated SCRs, is as small as $T_{SN}\sim 10^4$ yr and the typical magneticfield strength in SNRs as large as 30 $\mu$G. Both situations are howeverpossible as a result of field amplification through CR backreaction in theacceleration process. It is pointed out that accurate measurements of thelow-latitude diffuse Galactic \gr spectrum at TeV-energies can serve as aunique consistency test for CR origin from the Supernova Remnant population asa whole.Comment: To appear in Astrophysical Journa