A correlation between hard X-rays and neutrinos in radio-loud and radio-quiet AGN

The production mechanism of astrophysical high-energy neutrinos is not yet understood. A common assumption is that beamed relativistic outflows (jets) driven by accreting black holes are needed to accelerate particles to such high energies to produce high-energy neutrinos. Indeed, the first astrophysical high-energy neutrino source candidate identified by IceCube at a significance level of >3σ was a blazar – an AGN with an accreting supermassive black hole that drives a relativistic jet directed towards Earth. Recently, IceCube discovered strong evidence that Seyfert galaxies also emit neutrinos, which appears unrelated to jet activity. Here, we show that the neutrino–hard X-ray flux ratio of the blazar TXS 0506+056 is consistent with neutrino production in a γ-obscured region near the central supermassive black hole, with the X-ray flux corresponding to reprocessed γ-ray emission with flux comparable to that of neutrinos. Similar neutrino–hard X-ray flux ratios were found for three of IceCube's Seyfert galaxies, raising the possibility of a common neutrino production mechanism that may not involve a strong jet. We examine how future observations could test the jet origin of blazar neutrinos.