Modelling the Galactic very-high-energy $\gamma$-ray source population

Abstract

The High Energy Stereoscopic System (H.E.S.S.) Galactic plane survey (HGPS) is to date the most comprehensive census of Galactic $\gamma$-ray sources at very high energies (VHE; $100\mathrm{GeV}\le E\le 100\mathrm{TeV}$). As a consequence of the limited sensitivity of this survey, the 78 detected $\gamma$-ray sources comprise only a small and biased subsample of the overall population. Still, numerical modelling allows us to study the VHE $\gamma$-ray source population in the Milky Way based on this sample. In this work, several azimuth-symmetric and spiral-arm models are compared for spatial source distribution. The luminosity and radius function of the population are derived from the source properties of the HGPS data set and are corrected for the sensitivity bias of the HGPS. Based on these models, VHE source populations are simulated and the subsets of sources detectable according to the HGPS are compared with HGPS sources. The power-law indices of luminosity and radius functions are determined to range between $-1.6$ and $-1.9$ for luminosity and $-1.1$ and $-1.6$ for radius. Azimuth-symmetric distributions and a distribution following a four-arm spiral structure without Galactic bar describe the HGPS data reasonably well. The total number of Galactic VHE sources is predicted to be in the range from 800 to 7000 with a total luminosity and flux of $(1.6-6.3)\cdot 10^{36}$~ph~s${}^{-1}$ and $(3-15)\cdot 10^{-10}$~ph~cm${}^{-2}$~s${}^{-1}$, respectively. Depending on the model, the HGPS sample accounts for $(68-87)\%$ of the emission of the population in the scanned region. This suggests that unresolved sources represent a critical component of the diffuse emission measurable in the HGPS. With the foreseen jump in sensitivity of the Cherenkov Telescope Array, the number of detectable sources is predicted to increase by a factor between 5 - 9.

arXiv comment11 pages, 11 figures, accepted for publication in Astronomy & Astrophysics

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• Unresolved sources naturally contribute to PeV $\gamma$-ray diffuse emission observed by Tibet AS$\gamma$
• Decomposing the Origin of TeV-PeV Emission from the Galactic Plane: Implications of Multi-messenger Observations
• Population synthesis of pulsar wind nebulae and pulsar halos in the Milky Way -- Predicted contributions to the very-high-energy sky
• The contribution of Galactic TeV pulsar wind nebulae to Fermi-LAT diffuse emission
• Prospects for a survey of the Galactic plane with the Cherenkov Telescope Array
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• The Steady-State Multi-TeV Diffuse Gamma-Ray Emission Predicted with GALPROP and Prospects for the Cherenkov Telescope Array
• Cosmic-ray propagation under consideration of a spatially resolved source distribution
• The Making of Catalogues of Very-High-Energy γ-ray Sources
• LHAASO protons versus LHAASO diffuse gamma-rays: a consistency check
• The Origin of the Very-High-Energy Diffuse $\gamma$-Ray Emission: The Case for Galactic Source Cocoons
• The population of Galactic supernova remnants in the TeV range
• Estimatingthe Contribution of Galactic Neutrino Sources
• Search for neutrino signals correlated with LHAASO diffuse Galactic emission
• First constraints on axion-like particles from Galactic sub-PeV gamma rays
• Runaway stars and the Galactic supernova remnant landscape: non-thermal emission and observational evidence
• Interpreting the LHAASO Galactic diffuse emission data
• Search for Diffuse Galactic Neutrinos with the Full ANTARES Telescope Dataset
• Young Massive Star Clusters as TeV Emitters: Constraints from H.E.S.S. and LHAASO
• TeV-PeV Gamma-ray and Neutrino Emission in the Galactic Plane