1,721,110 research outputs found
A multi-messenger study of the total galactic high-energy neutrino emission
No full textA detailed multi-messenger study of the high-energy emission from the Galactic plane is possible nowadays thanks to the observations provided by gamma and neutrino telescopes. We show the potential of this approach by using the total gamma flux from the galactic plane measured by HESS at 1 TeV and in the longitude range -75- < l < 60-. We compare the HESS observational data with expectations for diffuse gamma emission, calculated by using different assumptions for the CR distribution in the Galaxy. We highlight the existence of an extended region of the galactic plane where the observed flux is substantially larger than the diffuse emission, thus calling for an additional contribution of comparable or larger intensity, possibly due to cumulative emission of resolved and unresolved gamma-ray sources. If this additional contribution is due to hadronic interactions, the considered region also produces a large neutrino flux and should be considered as a preferential target for the search of a galactic component in neutrino telescopes. We estimate the total contribution (i.e. including both diffuse and the source components) of this region to the IceCube HESE neutrino dataset as a function of the spectral index and energy cutoff of the sources, taking also into account the upper limit on galactic neutrino emission provided by Antares
Unveiling the Nature of Galactic TeV Sources with IceCube Results
No full textIceCube collaboration reported the first high-significance observation of the neutrino emission from the Galactic disk. The observed signal can be due to diffuse emission produced by cosmic rays interacting with interstellar gas but can also arise from a population of sources. In this paper, we evaluate both the diffuse and source contribution by taking advantage of gamma-ray observations and/or theoretical considerations. By comparing our expectations with IceCube measurements, we constrain the fraction of Galactic TeV gamma-ray sources (resolved and unresolved) with hadronic nature. In order to be compatible with the IceCube results, this fraction should be small, or the source proton energy cutoff should be well below the cosmic-ray proton knee. In particular, for a cutoff energy equal to 500 TeV, the fraction of hadronic sources should be less than ∼40% corresponding to a cumulative source flux Φ ν,s ≤ 2.6 × 10−10 cm−2 s−1 integrated in the 1-100 TeV energy range. This fraction reduces to ∼20% for energy cutoff reaching the cosmic-ray proton knee around 5 PeV
The fraction of muon tracks in cosmic neutrinos
No full textThe study of the distintive signatures of the ultra high energy events recently seen by IceCube can allow to single the neutrino origin out. The detection of tau neutrinos would be a clear way to prove that they come from cosmic distances, but at the highest energies currently seen, about 1 PeV, an experimental characterization of tau events is difficult. The study of the fraction of the muon tracks seems more promising. In fact, for any initial composition, because of the occurrence of flavor oscillations and despite their uncertainties, the fraction of muon tracks in the cosmic neutrinos is smaller than the one of atmospheric neutrinos, even hypothesizing an arbitrarily large contribution from charmed mesons. A good understanding of the detection efficiencies and the optimization of the analysis cuts, along with a reasonable increase in the statistics, should provide us with a significant test of the cosmic origin of these events
The contribution of Galactic TeV pulsar wind nebulae to Fermi large area telescope diffuse emission
Get PDFThe large-scale diffuse γ − ray flux observed by Fermi Large Area Telescope (Fermi-LAT) in the 1–100 GeV energy range, parameterized as ∝ E−Γ, has a spectral index Γ that depends on the distance from the Galactic center. This feature, if attributed to the diffuse emission produced by cosmic rays interactions with the interstellar gas, can be interpreted as the evidence of a progressive cosmic ray spectral hardening towards the Galactic center. This interpretation challenges the paradigm of uniform cosmic rays diffusion throughout the Galaxy. We report on the implications of TeV Pulsar Wind Nebulae observed by the High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey in the 1–100 TeV energy range for the interpretation of Fermi-LAT data. We argue that a relevant fraction of this population cannot be resolved by Fermi-LAT in the GeV domain providing a relevant contribution to the large-scale diffuse emission, ranging within ~4%–40% of the total diffuse γ-ray emission in the inner Galaxy. This additional component may account for a large part of the spectral index variation observed by Fermi-LAT, weakening the evidence of cosmic ray spectral hardening in the inner Galaxy
Probing galactic cosmic ray distribution with TeV gamma-ray sky
No full textThe distribution of cosmic rays in the Galaxy is still uncertain and this affects the expectations for the diffuse gamma-ray emission produced by hadronic interactions of cosmic rays with the interstellar gas. We evaluate the diffuse gamma-ray flux at TeV energies by considering different assumptions for the cosmic ray distribution, including the recently emerged possibility of a decreasing cosmic ray spectral index in the inner Galaxy. The diffuse emission from the galactic central region (i.e. in the longitude range | l | ≤ 60) changes in the different scenarios by a relatively large factor and can be probed by TeV scale gamma-ray observations. By comparing the total flux produced by diffuse emission and point-like and extended sources resolved by HESS with the gamma-ray flux observed by Argo-YBJ, HESS, HAWC and Milagro, we show that experimental data can already discriminate among different hyphoteses for cosmic ray distribution. The constraints can be strengthened if the contribution of sources not resolved by HESS is taken into account
The galactic diffuse high energy neutrino flux
Get PDFWe calculate the diffuse high energy neutrino flux produced by the interactions of cosmic rays with the gas contained in our Galaxy. In order to quantify the role of uncertainties in the cosmic ray propagation models, we consider three different assumptions for the cosmic ray distribution in the Galaxy. We provide expectations for the spectrum and the angular dependence of the diffuse galactic neutrino flux. We compare our predictions with the isotropic flux required to explain the 54 HESE events observed by IceCube in four years data taking
The TeV Gamma-Ray Luminosity of the Milky Way and the Contribution of H.E.S.S. Unresolved Sources to Very High Energy Diffuse Emission
Get PDFH.E.S.S. has recently completed the first systematic survey of the Galactic plane in the TeV energy domain. We analyze the flux, latitude, and longitude distributions of γ-ray sources observed by H.E.S.S. in order to infer the properties of the Galactic TeV source population. We show that the total Milky Way luminosity in the 1-100 TeV energy range is. Evaluating the cumulative flux expected at Earth by the considered population, we show that H.E.S.S. unresolved sources provide a relevant contribution to the diffuse Galactic emission. Finally, in the hypothesis that the majority of bright sources detected by H.E.S.S. are powered by pulsar activity, like, e.g., pulsar wind nebulae or TeV halos, we estimate the main properties of the pulsar population
- …
