Gamma-Rays from Pion Production in the Milky Way Halo

Low-energy cosmic rays (CRs) below the ``knee'' are believed to be produced by galactic sources (supernova remnant shocks, pulsars) and are trapped in the galactic magnetic fields whereas higher-energy CRs, up to $\sim10^{18}$~eV, are leaking from the Galaxy. In a recent work, a model of the ``Galactosphere'' --- the up-scaled analog of the Heliosphere --- has been suggested to exist around the Milky Way and produce lower-energy CRs at the galactic termination and bow shocks. We proposed the observational test of the model via pion-produced gamma-rays generated by these TeV ``anomalous extra-galactic CRs'' propagating through the Galactic halo and interacting with hydrogen gas in high-velocity clouds (HVCs) and inside the Galaxy. We estimate the peak of the gamma-ray spectrum to be in the 10~GeV range, hence the signal from HVCs and the north-south galactic asymmetry of the gamma-ray background are potentially detectable by LAT on board of FermiGST.