2020A&A...637A..44N

Context. Measurement of diffuse γ-ray emission from the Milky Way with Imaging Atmospheric Cherenkov Telescopes (IACT) is difficult because of the high level of charged cosmic ray background and the small field of view.
Aims. We show that such a measurement is nevertheless possible in the energy band 10-100TeV.
Methods. The minimal charged particle background for IACTs is achieved by selecting the events to be used for the analyses of the cosmic ray electrons. Tight cuts on the event quality in these event selections allow us to obtain a sufficiently low background level to allow measurement of the diffuse Galactic γ-ray flux above 10TeV. We calculated the sensitivities of different types of IACT arrays for the Galactic diffuse emission measurements and compared them with the diffuse γ-ray flux from different parts of the sky measured by the Fermi Large Area Telescope below 3TeV and with the astrophysical neutrino signal measured by IceCube telescope.
Results. We show that deep exposure of existing IACT systems is sufficient for detection of the diffuse flux from all the Galactic Plane up to Galactic latitude |b|∼5°. The Medium Size Telescope array of the CTA will be able to detect the diffuse flux up 30° Galactic latitude. Its sensitivity will be sufficient for detection of the γ-ray counterpart of the Galactic component of the IceCube astrophysical neutrino signal above 10TeV. We also propose that a dedicated IACT system composed of small but wide-field-of-view telescopes could be used to map the 10-100TeV diffuse γ-ray emission from across the whole sky.
Conclusions. Detection and detailed study of diffuse Galactic γ-ray emission in the previously unexplored 10-100TeV energy range is possible with the IACT technique. This is important for identification of the Galactic component of the astrophysical neutrino signal and for understanding the propagation of cosmic rays in the interstellar medium.