Since early 2016, the IceCube collaboration is promptly distributing alerts of high-energy neutrino detections in order to allow follow-up searches for possible counterparts at the neutrino position. Finding such counterparts would provide important clues on the origin of the high-energy neutrinos and, by proxy, on the nature of the high-energy cosmic ray accelerators, one of the most important and long-standing puzzles of high-energy astrophysics. We ask for pointed ToO observation of the HESE (High Energy Starting Events) and EHE (Extremely High Energy) neutrinos detected by IceCube and reported either in pub-lic or in private GCNs. We will employ the best available knowledge of the INTEGRAL instruments and our expertise in multimessenger transient searches to hunt for a possible hard X-ray and gamma-ray counterparts. In absence of a detection, we will set the most stringent upper limits.We intend to promptly communicate the results of our ToOs to the general community, thus supporting additional multiwavelength follow-ups and increasing the visibility of the INTEGRAL contribution to the searches of multimessenger transients.
The INTEGRAL (International Gamma-Ray Astrophysics Laboratory) mission, launched by the European Space Agency (ESA) on October 17, 2002, was designed to study high-energy phenomena in the universe. INTEGRAL was operating until february 2025 and it was equipped with three high-energy instruments: the Imager on Board the INTEGRAL Satellite (IBIS), the Spectrometer on INTEGRAL (SPI), and the JEM-X (Joint European Monitor for X-rays). Its Optical Monitoring Camera (OMC) provided optical V-band magnitude measurements, complementing the high-energy observations.
European Space Agency, Savchenko, 2026, 'Proposal for INTEGRAL ToO observations of IceCube neutrinos', 1.0, European Space Agency, https://doi.org/10.57780/esa-0tf99uw
