Describing correlated observations of neutrinos and gamma-ray flares from the blazar TXS 0506+056 with a proton blazar model

Abstract

Recent detection of the neutrino event IceCube-170922A by the IceCube Observatory from the blazar TXS $0506+056$ in the state of enhanced gamma-ray emission indicates the acceleration of cosmic rays in the blazar jet. The nondetection of the broadline emission in the optical spectrum of TXS $0506+056$ and other BL Lac objects suggests that external photon emissions are weak, and hence, photo-meson ($p\ensuremath{\gamma}$) interaction may not be a favored mechanism for high-energy neutrino production. The lack of broadline signatures also creates doubt about the presence of a high density cloud in the vicinity of the supermassive black hole of TXS $0506+056$ and consequently raised question on hadronuclear ($pp$) interaction interpretation like relativistic jet meets with high density cloud. Here we demonstrate that nonrelativistic protons in the proton blazar model---those that come into existence under the charge neutrality condition of the blazar jet---offer sufficient target matter for $pp$ interaction with shock-accelerated protons, and consequently, the model can describe consistently the observed high-energy gamma rays and neutrino signal from the blazar TXS $0506+056$.