Probing the galactic cosmic-ray density with current and future $\gamma$-ray instruments

Abstract

Cosmic Rays (CRs) propagating through dense molecular clouds (MCs) produce gamma rays which carry direct information about the CR distribution throughout the Galaxy. Observations of gamma rays in different energy bands allow exploration of the average CR density in the Galactic Disk, the so-called level of the "CR Sea". Fermi-LAT observations have demonstrated the method's feasibility based on two dozen MCs in our Galaxy. However, the potential of Fermi-LAT is limited by the most massive and relatively nearby MCs; thus, the current observations cover only a tiny fraction of the Milky Way. In this paper, we study the prospects of expanding the CR measurements to very and ultra-high energies and remote parts of the Galaxy with the current and next-generation detectors. Based on calculations of fluxes expected from MCs, we formulate the requirements to the sensitivity of the post-Fermi-LAT detectors to map GeV-TeV CRs in the Galactic Disk. We also explore the potential of the current and future air-shower and atmospheric Cherenkov telescope arrays for the extension of CR studies to multi-TeV and PeV energy bands. We demonstrate that the improvement of the Fermi-LAT sensitivity by a factor of a few would allow a dramatic increase in the number of detectable MCs covering almost the entire Galaxy. The recently completed LHAASO should be able to take the first CR probes at PeV energies in the coming five years or so.

9 pages, 8 figures

References in corpus (11)

• Physical properties of molecular clouds for the entire Milky Way disk
• Background Modelling in Very-High-Energy gamma-ray Astronomy
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• First Detection of sub-PeV Diffuse Gamma Rays from the Galactic Disk: Evidence for Ubiquitous Galactic Cosmic Rays beyond PeV Energies
• Gamma rays from molecular clouds
• Validation of open-source science tools and background model construction in $\gamma$-ray astronomy
• On particle acceleration and transport in plasmas in the Galaxy: theory and observations
• On the gamma-ray emission of W44 and its surroundings
• Probing the Cosmic Ray density in the inner Galaxy
• Evidence of Cosmic-Ray Excess from Local Giant Molecular Clouds
• Using Interstellar Clouds to Search for Galactic PeVatrons: Gamma-ray Signatures from Supernova Remnants

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• Detailed Analysis of the TeV γ-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192
• Are Kronberger 80 and/or Kronberger 82 regions PeVatron candidates for LHAASO J2108+5157?