Cosmic Neutrinos from Temporarily Gamma-suppressed Blazars
Emma Kun, Imre Bartos, Julia Becker Tjus, Peter L. Biermann, Francis Halzen, György Mező
Abstract
Abstract Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and neutrino production are still uncertain. Recent studies found that when transparent to γ -rays, γ -flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which γ -ray emission is suppressed during efficient neutrino production. A large proton and target photon density helps produce neutrinos while temporarily suppressing the observable γ -emission due to a large γ γ opacity. We show that the Fermi-LAT γ -flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40 m Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and γ fluxes are correlated for both low and high states. This points to an active outflow that is γ -suppressed at the time of neutrino production. We find similar local γ -suppression in other blazars, including in MAGIC’s TeV flux of TXS 0506+056 and Fermi-LAT’s flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary γ -suppression, neutrino–blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube’s diffuse neutrino flux possibly with already existing data.