1,720,973 research outputs found
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 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
Unresolved Sources Naturally Contribute to PeV Gamma-Ray Diffuse Emission Observed by Tibet AS γ
Get PDFThe Tibet ASγ experiment provided the first measurement of the total diffuse gamma-ray emission from the Galactic disk in the sub-PeV energy range. Based on the analysis of TeV sources included in the H.E.S.S. Galactic Plane Survey catalog, we predict the expected contribution of unresolved pulsar-powered sources in the two angular windows of the Galactic plane observed by Tibet ASγ. We show that the sum of this additional diffuse component due to unresolved sources and the truly diffuse emission, due to cosmic-ray interaction with the interstellar medium, well saturates the Tibet data, without the need to introduce a progressive hardening of the cosmic-ray spectrum toward the Galactic center
The Galactic Population of Pulsar Wind Nebulae and the Contribution of Its Unresolved Component to the Diffuse High-Energy Gamma-ray Emission
No full textIn this work, we provide a phenomenological description of the population of galactic TeV pulsar wind nebulae (PWNe) based on suitable assumptions for their space and luminosity distribution. We constrain the general features of this population by assuming that it accounts for the majority of bright sources observed by H.E.S.S. Namely, we determine the maximal luminosity and fading time of PWNe (or, equivalently, the initial period and magnetic field of the pulsar powering the observed emission) by performing a statistical analysis of bright sources in the H.E.S.S. galactic plane survey. This allows us to estimate the total luminosity and flux produced by galactic TeV PWNe. We also evaluate the cumulative emission from PWNe that cannot be resolved by H.E.S.S., showing that this contribution can be as large as ∼40% of the total flux from resolved sources. We argue that also in the GeV domain, a relevant fraction of this population cannot be resolved by Fermi-LAT, providing a non-negligible contribution to the large-scale diffuse emission in the inner galaxy. This additional component could naturally 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. Finally, the same result is obtained for PeV energy, for which the sum of the diffuse component, due to unresolved PWNe, and the truly diffuse emission well saturates the recent Tibet AS- (Formula presented.) data, without the need to introduce a progressive hardening of the cosmic-ray spectrum toward the galactic centre
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
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 TeV gamma-ray source population of the Milky-Way
No full textIn this work we perform a population study of the H.E.S.S. Galactic Plane Survey (HGPS) catalogue. Namely, we analyze the flux, latitude and longitude distributions of gamma-ray sources detected by H.E.S.S. with the goal of inferring the main properties of galactic TeV sources population. We show that the total Milky Way luminosity in the 1-100 TeV energy range is relatively well constrained by H.E.S.S. data, obtaining LMW = 1.7+-0054 × 1037ergs s-1. The total Galactic flux in the H.E.S.S. observational window is Φtot = 3.8+-1100 × 10-10cm-2 s-1. The above results allows us to estimate the flux produced by sources not resolved by H.E.S.S. These sources, which are too faint (or too extended) to be detected by H.E.S.S., contribute to the large-scale diffuse signal observed at the TeV range. We show that unresolved source contribution is not negligible (about 60% of the resolved signal measured by H.E.S.S.) and potentially responsible for a large fraction of the diffuse-large scale gamma-ray signal observed by H.E.S.S. and other experiments in the TeV domain. 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: we obtain a constrain on the fading time τ, the initial period P0 and the magnetic field B
Can the TeV gamma-ray sky probe the galactic cosmic ray distribution?
No full textWe evaluate the diffuse gamma-ray flux at TeV energies produced by hadronic interactions of cosmic rays with the gas contained in the galactic disk. We consider different assumptions for the cosmic ray distribution, including the recently emerged possibility of a harder cosmic ray spectrum in the inner Galaxy. We show that observational data provided by Argo-YBJ, HESS, HAWC and Milagro, can already discriminate among different hyphoteses. The constraints can be strengthened if the contribution of sources not resolved by HESS is taken into account
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