Speaker
Description
Standard cosmic ray (CR) propagation models that assume neither a time-independent source distribution nor a location-independent diffusion cannot give rise to spatially dependent CR (and hence γ-ray) spectral slopes. Yet, recent observations by Fermi-LAT exhibit a hardening of the γ-ray spectrum between the Sagittarius and Carina tangents, and a further hardening at a few degrees above and below the Galactic plane. Here, we study a model in which the distribution of CR sources is concentrated in the galactic spiral arms, and in particular, that these arms are dynamic. The model has been successful in explaining secondary to primary ratios (e.g., B/C, sub-Iron/Iron, positrons) as well as long term variations in the CR flux over geological time scales. We find unique signatures that agree with the Fermi-LAT observations and also provides a physical explanation to the difference between the local CR spectral slope and the CR slope inferred from the average γ-ray spectrum.
