  Recent observations of high-energy neutrinos by IceCube and gamma rays by the
Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that
neutrinos are produced in gamma-ray opaque environments in the vicinity of
supermassive black holes. In this work, we present 20 MeV - 1 TeV spectra of
three Seyfert galaxies whose nuclei are predicted to be active in neutrinos,
NGC 4151, NGC 4945 and the Circinus galaxy, using 14.4 yr of the Fermi LAT
data. In particular, we find evidence of sub-GeV excess emission that can be
attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These
spectral features are consistent with predictions of the magnetically powered
corona model, and we argue that NGC 4945 is among the brightest neutrino active
galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast
to other reported results, we do not detect gamma rays from NGC 4151, which
constrains neutrino emission from the accretion shock model. Future neutrino
detectors such as IceCube-Gen2 and MeV gamma-ray telescopes such as AMEGO-X
will be crucial for discriminating among the theoretical models.
