Neutrino Fluxes from Active Galaxies: A Model‐Independent Estimate

There are tantalizing hints that jets, powered by supermassive black holes atthe center of active galaxies, are true cosmic proton accelerators. Theyproduce photons of TeV energy, possible higher, and may be the enigmatic sourceof the highest energy cosmic rays. Photoproduction of neutral pions byaccelerated protons on UV light is the source of the highest energy photons, inwhich most of the bolometric luminosity of the galaxy may be emitted. The casethat proton beams power active galaxies is, however, far from conclusive.Neutrinos from the decay of charged pions represent an uncontrovertiblesignature for the proton induced cascades. We show that their flux can beestimated by model-independent methods, based on dimensional analysis andtextbook particle physics. Our calculations also demonstrate why differentmodels for the proton blazar yield very similar results for the neutrino flux,consistent with the ones obtained here.