Realtime Neutrino Alerts for Multi-Messenger Astrophysics: the Gamma-Ray Follow-Up (GFU) platform for IceCube.

Since the discovery of a diffuse flux of astrophysical neutrinos in 2013, high-energy neutrino Astroparticle Physics has undergone a rapid development in recent years, driven by the improved sensitivity of IceCube and the new neutrino telescopes becoming operative. Neutrino telescopes play a key role in the multi-messenger hunt for hadronic accelerators that produce the highest-energy detected cosmic rays and neutrinos. As they have a complete field of view of the full sky with almost constant up-time, they can act as sentinels monitoring the sky for exceptional transient events, with the aim of alerting the astrophysical community to engage follow-up observations that could help unveil the hidden mechanisms of cosmic accelerators. The Gamma-ray Follow-Up (GFU) platform has been alerting partner telescopes at the detection of significant clusters in space and time of neutrino events by monitoring both a list of preselected sources and the entire sky. This work presents the first technical validation analysis since the ignition of the GFU-cluster alert stream, and provides an offline search for neutrino flares over 11.5 years of data. Both analyses support the ongoing effort to transition GFU-cluster alerts toward a public distribution, with the aim of maximizing the scientific reach of the program. In view of this, a new list of sources for targeted monitoring is developed and presented in light of the most updated insights on promising neutrino emitters, and models of emission mechanisms favoring sources that are to some extent opaque to the γ-rays co-produced with the high-energy neutrinos. This work therefore provides an original contribution to the consolidation of the GFU platform’s role within the multimessenger landscape, at a time when neutrino astronomy is rapidly evolving and in preparation for the next generation of facilities.