PeV neutrinos from interactions of cosmic rays with the interstellar medium in the Galaxy

Abstract

We present a self-consistent interpretation of the very high-energy neutrino signal from the direction of the inner Galaxy, which is a part of the astronomical neutrino signal reported by IceCube. We demonstrate that an estimate of the neutrino flux in the E > 100 TeV energy range lies at the high-energy power-law extrapolation of the spectrum of diffuse γ-ray emission from the galactic ridge, as observed by the Fermi telescope. This suggests that IceCube neutrino and Fermi/LAT γ-ray fluxes are both produced in interactions of cosmic rays with the interstellar medium in the Norma arm and/or in the galactic bar. Cosmic rays responsible for the (γ ray) and neutrino flux are characterized by a hard spectrum with the slope harder than −2.4 and cutoff energy higher than 10 PeV.

Neutrino fluxes from the Galactic plane and the ANTARES limit

“…For comparison, assuming an E −2.4 spectrum, the normalisation of an IceCube-like flux producing 3 or more events from a region in the sky of 0.1 sr is larger than 2.0 10 −5 GeV −1 cm −2 s −1 sr −1 and any of these scenarios can be rejected. Figure 1 -left, compares the obtained sensitivity in the Galactic Plane region to the expected neutrino flux from CR propagation of [12] and the extrapolated Fermi spectrum of [10]. This sensitivity holds in the energy range 3 TeV -300 TeV, which contains the central 90% of the expected signal.…”

“…Assuming that a certain fraction of the observed diffuse flux in the central region of the Galaxy originates from hadronic mechanisms, the neutrino yield from CR propagation can be calculated. Different predictions are available such in [10][11][12]. Each of these provides a different description of the expected neutrino flux, with an overall normalisation that can vary by one order of magnitude.…”

Astrophysical origin of high-energy cosmic neutrinos

“…But signifiant event clustering around the Galactic plane is not seen at present [23]. However, nearby sources in the local spiral arm of the Milky Way may appear at higher latitudes [78]. There is a fluctuation at longitudes ∼ 240 • , although no apparent neutrino clustering is found in the opposite direction [23].…”

A Galactic Halo Origin of the Neutrinos Detected by IceCube

“…The origin of the neutrinos detected by IceCube presently remains unknown. Both Galactic [3][4][5] and extragalactic [6,7] scenarios of their production have been proposed, with a tendency to disfavor Galactic models other than those involving a connection with the Fermi bubble structures. These structures, whose existence were only recently disclosed both in γ-rays and radio [8,9], extend well outside the Galactic plane region and may well house a significant population of cosmic ray (CR) particles.…”