A Test of the Hadronic Origin of γ-Rays from Blazars with Follow-up up to a Month Later of IceCube Alerts with Imaging Air Cherenkov Telescopes

The sources of IceCube neutrinos are as yet unknown. The multimessenger observation of their emission in γ-rays can be a guide to their identification, as exemplified by the case of TXS 0506+056. We suggest a new method of searching for γ-rays with Imaging Air Cherenkov Telescopes from sources coinciding with possible astrophysical neutrinos. We propose that searches of γ-rays be extended from the current practice of only a few days to up to one month from a neutrino alert. We test this strategy on simulated sources modeled after the blazar TXS 0506+056, emitting neutrinos and γ-rays via photohadronic interactions: the γ-rays are subsequently reprocessed in the VHE range. Using MAGIC as a benchmark example, we show that current Cherenkov Telescopes should be able to detect γ-ray counterparts to neutrino alerts with a rate of approximately one per year. It has been proposed that the high-energy diffuse neutrino flux can be explained by ~5% of all blazars flaring in neutrinos once every 10 yr, with a neutrino luminosity similar to that of TXS 0506+056 during the 2014-2015 neutrino flare. The implementation of our strategy could lead, over a timescale of one or a few years, either to the detection of this subclass of blazars contributing to the diffuse neutrino flux or to a constraint on this model.