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Neutrino-emitting blazars may accelerate cosmic ray (CR) protons at the inner regions of the jet, where most of the magnetic energy is likely to be dissipated. In this picture, the spectrum of the neutrino output is shaped by the soft photon fields that the parent hadrons encounter before leaving the source. In this work, we build a lepto-hadronic emission model based on particle acceleration by magnetic reconnection along the jet propagation axis, in the transition from magnetically to kinetically dominated flow. We employ the reconnection striped jet model to obtain the jet properties at three characteristic emission regions and derive the associated electromagnetic and neutrino output. We also perform Monte Carlo simulations for the propagation of CR protons within the jet as an alternative method for calculating the neutrino flux. We apply this emission model to interpret the 2017 multi-messenger event from the blazar TXS 0506+056 and we also discuss applications of the model in the context of flat-spectrum radio quasars and BL Lac objects.

The origin of magnetic fields in the Universe is an open problem. Seed magnetic fields possibly produced in early times may have survived up to the present day close to their original form, providing an untapped window to the primeval Universe. The recent observations of high-energy neutrinos from the blazar TXS 0506+056 in association with an electromagnetic counterpart in a broad range of wavelengths can be used to probe intrinsic properties of this object and the traversed medium. Here we show that intergalactic magnetic fields (IGMFs) can affect the intrinsic spectral properties of this object reconstructed from observations. In particular, we point out that the reconstructed maximum gamma-ray energy of TXS 0506+056 can be significantly higher if IGMFs are strong. Finally, we use this flare to constrain both the magnetic-field strength and the coherence length of IGMFs.