Impact of Multimessenger Spectral Modeling on Blazar–Neutrino Associations

Abstract Blazars are interesting source candidates for astrophysical neutrino emission. Multimessenger leptohadronic models based on proton–photon ( pγ ) interactions result in predictions for the neutrino spectra (“ pγ spectra”), which are typically strongly peaked at PeV energies. In contrast, statistical analyses looking to associate blazars and high-energy neutrinos often assume a power-law spectral shape, putting the emphasis at lower energies. We aim to examine the impact of such spectral modeling assumptions on the associations of neutrinos with blazars. We use hierarchical_nu , a Bayesian framework for point-source searches, and incorporate the theoretical predictions for neutrino spectra through a dedicated spectral model and priors on the relevant parameters. Our spectral model is based on recent predictions for a selection of intermediate and high synchrotron peaked blazars that have been found to be spatially close to high-energy events detected by IceCube. We apply our model to the 10 yr of publicly available muon track IceCube data aimed at point-source searches, focusing on the Northern Hemisphere. Out of 29 source candidates, we find five sources, including TXS 0506+056, that have an association probability P assoc > 0.5 to at least one event. The pγ spectra typically lead to a lower overall number of associated events compared to the power-law case, but retain or even enhance strong associations to high-energy events. Our results demonstrate that including more information from theoretical predictions can allow for more interpretable source–neutrino connections.