We explore the concept of liquid Argon time projection chamber (TPC) for γ-ray astronomy in the 100 M eV -1 T eV energy range. We propose a basic layout for such a telescope called MAST. Using a last-generation rocket such as Falcon Heavy, it is possible to launch a detector with the effective area and the differential sensitivity about one order of magnitude better than the Fermi-LAT ones. At the same time, the MAST concept allows for an excellent angular resolution, 3-10 times better than the Fermi-LAT one depending on the energy, and good energy resolution (≈ 20 % at 100 M eV and 6-10 % for the 10 GeV -1 T eV energy range). We show that such a telescope would be instrumental in a broad range of long-standing astrophysical problems.

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Galactic sites of acceleration of cosmic rays to energies of order 1015 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In 2020 November, the IceCube neutrino observatory reported an ∼150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1σ (post-trial) excess of atmospheric air showers from the same direction, observed by the Carpet–2 experiment and consistent with a few months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma-rays in a Galactic source.

Abstarct Properties of the extragalactic magnetic field (EGMF) outside of clusters and filaments of the large-scale structure are essentially unknown. The EGMF could be probed with γ-ray observations of distant (redshift z > 0.1) blazars. TeV γ rays from these sources are strongly absorbed on extragalactic background light photons; secondary electrons and positrons produce cascade γ rays with the observable flux dependent on EGMF parameters. We put constraints on the EGMF strength using 145 months of Fermi-LAT observations of the blazars 1ES 1218+304, 1ES 1101-232, and 1ES 0347-121, and imaging atmospheric Cherenkov telescope observations of the same sources. We perform a series of full direct Monte Carlo simulations of intergalactic electromagnetic cascades with the ELMAG 3.01 code and construct a model of the observable spectra inside the point spread functions of the observing instruments for a range of EGMF strengths. We compare the observed spectra with the models for various values of the EGMF strength B and calculate the exclusion statistical significance for every value of B. We find that the values of the EGMF strength B ≤ 10−17 G are excluded at a high level of the statistical significance Z > 4σ for all the four options of the intrinsic spectral shape considered (power-law, power-law with exponential cutoff, log-parabola, log-parabola with exponential cutoff). The value of B = 10−16 G is not excluded; it is still a viable option of the EGMF strength. These results were obtained for the case of steady sources.