A Neutral Beam Model for High-energy Neutrino Emission from the Blazar TXS 0506+056

The IceCube collaboration reported an ∼3.5σ excess of 13 ± 5 neutrino events in the direction of the blazar TXS 0506+056 during an ∼6 month period in 2014-2015, as well as the (∼3σ) detection of a high-energy muon neutrino during an electromagnetic flare in 2017. We explore the possibility that the 2014-2015 neutrino excess and the 2017 multimessenger flare are both explained in a common physical framework that relies on the emergence of a relativistic neutral beam in the blazar jet due to interactions of accelerated cosmic rays (CRs) with photons. We demonstrate that the neutral beam model provides an explanation for the 2014-2015 neutrino excess without violating X-ray and γ-ray constraints and yields results consistent with the detection of one high-energy neutrino during the 2017 flare. If both neutrino associations with TXS 05065+056 are real, our model requires that (i) the composition of accelerated CRs is light, with a ratio of helium nuclei to protons ⪆5; (ii) a luminous external photon field (∼10⁴⁶ erg s^-1) variable (on yearlong timescales) is present; and (iii) the CR injection luminosity, as well as the properties of the dissipation region (i.e., Lorentz factor, magnetic field, and size), vary on yearlong timescales.