The IceCube collaboration detected high-energy neutrinos, considered a milestone in astrophysics, back in 2013. These kinds of neutrinos have energies spanning from 30 TeV up to 1 PeV and are distributed isotropically, indicating their origins in the distant universe. While quite a few theoretical models are trying to explain these fluxes of cosmic neutrinos, the exact sources are yet unknown.
The breakthrough came in 2018 when the IceCube collaboration, together with electromagnetic observatories, identified what could well be a source: the flare of the blazar TXS 0506+056. The observation marked the first evidence of a blazar as a cosmic neutrino factory. Further analysis showed that blazars can account for only about 30% of the cosmic neutrino background flux observed, and thus most of the sources are still unknown.
Only recently, a decade-long survey undertaken by IceCube was able to report the detection of a neutrino excess-hot spot in the direction of the nearest Seyfert 2 galaxy, NGC 1068, at a confidence level of 2.9 σ. The Seyfert galaxies, including obscured central engines, are much more surface-dense compared to blazars. Indeed, this may be an indication that Seyfert galaxies dominate the cosmic neutrino sky. The harder task now will be that of determining the way neutrals are produced in these galaxies.
Gamma-ray and neutrino measurements are correlated to understand the neutrino production mechanism. Fermi-MAGIC observatories have detected GeV-TeV gamma-ray photons from NGC 1068. However, the observed neutrino flux exceeds the gamma-ray flux beyond simple hadronuclear or photomeson interpretation processes.
Models for the neutrino excess from NGC 1068 have been proposed based on theoretical ideas involving accretion disk coronae, interactions of broad-line-region clouds with accretion disks, and galactic cosmic-ray halos. All these models are burdened by large uncertainties, and a deeper understanding of the properties of AGN coronae is highly desired.
With the development of radio and X-ray telescopes, it has been possible to measure several physical parameters related to electron density, temperature, size, and magnetic field strength in the coronae of AGN. The ALMA observations also provided solid evidence for the presence of a weak non-thermal coronal activity, thus confirming that high-energy particles are indeed part of the AGN coronae.
Meanwhile, long-duration gamma-ray bursts have allowed the study of afterglows, and indeed observations of “dark” GRBs-obscured by dust-have detected radio afterglows that shed light on the high line-of-sight dust extinctions, which imply that the high extinction levels arise from a larger-scale patchy dust distribution.
These discoveries have big implications for military purposes. Knowledge of the origins and mechanisms that generate high-energy neutrinos and gamma-ray bursts would further our understanding of the cosmos with new potential improvements in space surveillance and defense technologies. As we continue to unravel the mysteries of the universe, the nexus of astrophysics and military science will no doubt yield new strategic insights.