Neutrino signal from extended Galactic sources in IceCube

Abstract

Context. The Galactic plane is the brightest source of γ rays in the sky. It should also be one of the brightest very-high-energy neutrino sources, if a neutrino flux comparable to the γ-ray flux is produced by the cosmic ray interactions in the interstellar medium. Aims. We explore the detectability of the neutrino flux from the entire Galactic plane or from a part of it with the IceCube neutrino detector. Methods. We calculated the normalization and the spectral index of the neutrino power-law spectrum from different regions of the Galactic plane, based on the observed spectral characteristics of the pion decay γ-ray diffuse emission observed by the Fermi/LAT telescope in the energy band above 100 GeV. We compared the neutrino flux calculated in this way with the sensitivity of IceCube for the detection of extended sources. Results. Assuming a binned extended source analysis method, we find that the only possible evidence of neutrino emission for sources located in the northern hemisphere after 20 years of exposure is from the Cygnus region. For other parts of the Galactic plane even a 20 year exposure with IceCube is not sufficient for the detection. Taking into account marginal significance of the detectable source in the Cygnus region, we find a precise position and size of the source region that optimizes the signal-to-noise ratio for neutrinos. We also calculated the low-energy threshold above which the neutrino signal can be detected with the highest signal-to-noise ratio. This calculation of precise source position, size, and energy range, based on the γ-ray data, can be used to remove the so-called trial factor in the analysis of the real neutrino data of IceCube. We notice that the diffuse neutrino emission from the inner Galactic plane in the southern hemisphere is much brighter. A neutrino detector with characteristics equivalent to IceCube, but placed at the northern hemisphere (such as KM3NeT), would detect several isolated neutrino sources in the Galactic plane with just a five-year exposure at the 5σ level. Their discovery would identify the cosmic ray sources in the Galaxy that have been active during the last 10 4 years. Conclusions. The detection of the diffuse neutrino emission from cosmic ray interactions in the Galactic disk is challenging, but marginally feasible with a 20 year exposure by IceCube. Dramatically shorter (2-5 yr) exposure times would be required for the Galactic plane signal detection with an IceCube-like neutrino detector in the northern hemisphere.

Constraining the production of cosmic rays by pulsars

“…[18] led to the conclusion that gamma-ray halos should exist around nearly all young pulsars with a spin-down age T SD 30 kyr. The observations of the very high-energy neutrinos reported by IceCube [25] can also be consistently interpreted within this scenario [26,27]. All of these pieces of evidence and their relevance for unveiling the puzzles of CRs suggest that the hypothesis of CR production by pulsars requires further investigation, which we perform in this paper.…”

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

“…This explains the improvement of sensitivity of IceCube to the signal from the inner galactic plane, compared to the estimate of Ref. [10] from the parts of the galactic plane centered at the positions of the sources HESS J1837-069 (an unidentified extended source), HESS J1825-137 (a pulsar wind nebula), a source close to the Galactic center supermassive black hole and/or G 0.9 þ 0.1 composite supernova remnant and an unidentified extended source HESS J1632-478. To identify the most probable candidate(s) for the sources of observed neutrinos, we have combined the measured spectrum of γ-ray emission from the hard and bright sources consistent with the IceCube event cluster and an estimate of the neutrino flux from the IceCube data.…”

“…This means that the extrapolation of the γ-ray signal from the sub-TeV toward higher energies should provide a good estimate for the 100 TeV neutrino signal all along the galactic plane [10]. To verify the selfconsistency of the model in which the observed E > 100 TeV neutrinos at low galactic latitudes are coming from the cosmic ray interactions, we also extract the γ-ray spectrum and estimate the neutrino flux from the region −90°< l < −30°(see Fig.…”

Prospects for detecting galactic sources of cosmic neutrinos with IceCube: An update

“…For related studies of the neutrino emission from Milagro sources, see also Refs. [12,36,[40][41][42][43][44].…”