Active galactic nuclei (AGN) are promising candidate sources of high-energy astrophysical neutrinos, since they provide environments rich in matter and photon targets where cosmic-ray interactions may lead to the production of gamma rays and neutrinos. We searched for high-energy neutrino emission from AGN using the Swift-BAT Spectroscopic Survey catalog of hard X-ray sources and 12 yr of IceCube muon track data. First, upon performing a stacked search, no significant emission was found. Second, we searched for neutrinos from a list of 43 candidate sources and found an excess from the direction of two sources, the Seyfert galaxies NGC 1068 and NGC 4151. We observed NGC 1068 at flux Φνμ+‾νμ = 4.02+1.58-1.52 x 10-11 TeV−1 cm−2 s−1 normalized at 1 TeV, with a power-law spectral index γ = 3.10+0.26-0.22, consistent with previous IceCube results. The observation of a neutrino excess from the direction of NGC 4151 is at a posttrial significance of 2.9σ. If interpreted as an astrophysical signal, the excess observed from NGC 4151 corresponds to a flux Φνμ+‾νμ = 1.51+0.99-0.81 x 10-11 TeV−1 cm−2 s−1 normalized at 1 TeV and γ = 2.83+0.35-0.28.
For complete list of authors see http://dx.doi.org/10.3847/1538-4357/ada94b