Galactic PeV Neutrinos

IceCube experiment has detected two neutrinos with energies beween 1-10 PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiations. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos.Comment: 5 pages, version to be published in Astroparticle Physic

Prompt Emission of High Energy Photons from Gamma Ray Bursts

Within the internal shock scenario we consider different mechanisms of high energy ($>1$ MeV) photon production inside a Gamma Ray Burst (GRB) fireball and derive the expected high energy photon spectra from individual GRBs during the prompt phase. The photon spectra of leptonic and hadronic origins are compared within different sets of parameter regimes. Our results suggest that the high energy emission is dominated by the leptonic component if fraction of shock energy carried by electrons is not very small (e.g. $\epsilon_e > 10^{-3}$). For very small values of $\epsilon_e$ the hadronic emission component could be comparable to or even exceed the leptonic component in the GeV-TeV regime. However, in this case a much larger energy budget of the fireball is required to account for the same level of the observed sub-MeV spectrum. The fireballs are therefore extremely inefficient in radiation. For a canonical fireball bulk Lorentz factor (e.g. $\Gamma=400$), emissions above $\sim 10$ GeV are attenuated by two-photon pair production processes. For a fireball with an even higher Lorentz factor, the cutoff energy is higher, and emissions of 10 TeV - PeV due to $\pi^0$-decay can also escape from the internal shocks. The flux level is however too low to be detected by current TeV detectors, and these photons also suffer attenuation by external soft photons.Comment: 18 pages 10figures, version to be published in MNRA