Jet-cloud/star interaction as an interpretation of neutrino outburst from the blazar TXS 0506+056

Recently, a high-energy neutrino event IceCube-170922A in the spatial and temporal coincidence with the flaring gamma-ray blazar TXS 0506+056 was reported. A neutrino outburst between September 2014 and March 2015 was discovered in the same direction by a further investigation of $9.5$ years of IceCube data, while the blazar is in a quiescent state during the outburst with a gamma-ray flux only about one-fifth of the neutrino flux. In this letter, we propose the neutrino outburst originates from the interaction between a relativistic jet and a dense gas cloud which may be formed via the tidally disrupted envelope of a red giant being blown by the impact of the jet. Gamma-ray photons and electron/positron pairs that are produced correspondingly will induce electromagnetic cascades. Comptonization of the cascade emission inside the cloud forms an X-ray photon field with Wien distribution. GeV flux is suppressed due to the absorption by the Comptonized photon field and, as a result, a hard spectrum above 10 GeV is formed. The gamma-ray spectrum predicted in our model is consistent with the Fermi-LAT data of TXS 0506+056.Comment: 6 pages, 3 figure

Hadronic origin of prompt high-energy emission of gamma-ray bursts revisited: in the case of a limited maximum proton energy

The high-energy (> 100MeV) emission observed by Fermi-LAT during the prompt phase of some luminous gamma-ray bursts (GRBs) could arise from the cascade induced by interactions between accelerated protons and the radiation field of GRBs. The photomeson process, which is usually suggested to operate in such a hadronic explanation, requires a rather high proton energy (> 10^17eV) for an efficient interaction. However, whether GRBs can accelerate protons to such a high energy is far from guaranteed, although they have been suggested as the candidate source for ultrahigh-energy cosmic rays. In this work, we revisit the hadronic model for the prompt high-energy emission of GRBs with a smaller maximum proton energy than the usually adopted value estimated from the Bohm condition. In this case, the Bethe-Heitler pair production process becomes comparably important or even dominates over the photomeson process. We show that with a relatively low maximum proton energy with a Lorentz factor of 10^5 in the comoving frame, the cascade emission can still reproduce various types of high-energy spectrum of GRBs. For most GRBs without high-energy emission detected, the maximum proton energy could be even lower and relax the constraints on the parameters of GRB jet resulting from the fact of non-detection of GRB neutrinos by IceCube.Comment: 36 pages, 13 figures, accepted for publication in Ap