Speaker
Description
Cosmic rays can be accelerated both in a source or in intergalactic space, producing gamma rays and neutrinos. Furthermore, all cosmic rays that escape a source can potentially initiate particle cascades through interactions with the background radiation fields such as the cosmic-microwave background and the extragalactic background light. In September 2017, a high-energy neutrino event detected by IceCube (IceCube-170922A) was associated, at the 3σ level, with a gamma-ray flare from the blazar TXS 0506+056. This multi-messenger association remains, as per today, the most significant photon-neutrino association ever observed. Here we report on a new search for proton cascade emission in TXS 0506+056, using a combined data set from the Fermi Large Area Telescope and VERITAS. We compare the gamma-ray spectrum and neutrino observations with the predictions of cosmic-ray induced cascades in intergalactic space. We also apply a full statistical analysis to jointly determine the best-fit parameters of a proton emission spectrum describing the data and derive constraints on the proton escape luminosity, using state-of-the-art Monte Carlo simulations.
