On the Detectability of High-Energy Galactic Neutrino Sources

With the arrival of km3 volume scale neutrino detectors the chances to detect the first astronomical sources of TeV neutrinos will be dramatically increased. While the theoretical estimates of the neutrino fluxes contain large uncertainties, we can formulate the conditions for the detectability of certain neutrino sources phenomenologically. In fact, since most galactic neutrino sources are transparent for TeV γ-rays, their detectability implies a minimum flux of the accompanying γ-rays. For a typical energy-dependence of detection areas of km3 volume neutrino detectors, we obtain the quantitative condition Iγ(20 TeV) > 2 × 10−15 ph/cm2s, that thanks to the normalization of the γ-ray spectrum at 20 TeV appears to be quite robust, i.e. almost independent of the shape of energy spectrum of neutrinos. We remark that this condition is satisfied by the young supernova remnants RX J1713.7-3946 and RX J0852.0-4622 (Vela Jr) two of the strongest galactic γ-ray sources. The preliminary condition for the detectability of high energy neutrinos is that the bulk of γ-rays has a hadronic origin: A new way to test this hypothesis for RX J1713.7-3946 is proposed. Finally, we assess the relevance of a neutrino detector located in the Northern Hemisphere for the search for galactic neutrino sources. In particular, we argue that if the TeV neutrino sources correlate with the galactic mass distribution, the probability that some of them will be observed by a detector in the Mediterranean Sea is larger by a factor of 1.4-2.9 compared to the one of IceCube.