Nava, LaraLaraNavaBenyamin, DavidDavidBenyaminPiran, TsviTsviPiranShaviv, Nir J.Nir J.Shaviv2020-08-212020-08-2120170035-8711http://hdl.handle.net/20.500.12386/26764Most of the diffuse Galactic GeV γ-ray emission is produced via collisions of cosmic ray (CR) protons with ISM protons. As such the observed spectra of the γ-rays and the CRs should be strongly linked. Recent observations of Fermi-LAT exhibit a hardening of the γ-ray spectrum at around a hundred GeV, between the Sagittarius and Carina tangents, and a further hardening at a few degrees above and below the Galactic plane. However, standard CR propagation models that assume a time-independent source distribution and a location-independent diffusion cannot give rise to a spatially dependent CR (and hence γ-ray) spectral slopes. Here, we consider a dynamic spiral arm model in which the distribution of CR sources is concentrated in the (dynamic) spiral arms, and we study the effects of this model on the π<SUP>0</SUP>-decay-produced γ-ray spectra. Within this model, near the Galactic arms the observed γ-ray spectral slope is not trivially related to the CR injection spectrum and energy dependence of the diffusion coefficient. We find unique signatures that agree with the Fermi-LAT observations. This model also provides a physical explanation for the difference between the local CR spectral slope and the CR slope inferred from the average γ-ray spectrum.STAMPAenArticle10.1093/mnras/stw33462-s2.0-85018282785000398418600086https://academic.oup.com/mnras/article/466/3/3674/27363022017MNRAS.466.3674NFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation