Blazars as neutrinos factories

The recent detection of gravitational waves together with the discovery, few years ago, of an extraterrestrial component of high-energy neutrinos, inaugurate the era of multimessanger astrophysics. The relativistic effects owing to the beaming of the jet, that is pointing at us, make blazars the most energetic, persistent particle accelerators of the Universe. Recent observations show the evidence for a possible positional correlation between the neutrino directions detected by IceCube and the position of a flaring BL Lac object (the case of TXS0506+056). Based on a simple theoretically-motivated framework, we postulated a direct proportionality between high-energy gamma-ray and neutrino fluxes from BL Lac objects. The non-detection of high-energy neutrinos associated to Mkn421, and more in general to the most brightest gamma-ray BL Lacs, leads us to investigate on the photons target density involved in the neutrino production. We discuss a scenario that explain the neutrino emission from TXS disfavouring the brightest gamma-ray sources.