Target of Opportunity searches for very high energy neutrino sources using the Cherenkov Telescope onboard EUSO-SPB2*

As part of the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission launched from Wanaka NZ on May 13 2023, we planned Target of Opportunity (ToO) observations to follow up on possible sources of PeV-scale neutrinos. We pointed the onboard Cherenkov Telescope (CT) just below Earth's horizon to catch sources' paths across the sky. By using the earth as a tau-neutrino to tau-lepton converter, the CT looked for optical EAS signals induced by tau-lepton decays. The CT has a field of view of 6.4° x 12.8°. Possible neutrino source candidates include gamma ray bursts, tidal disruption events and other bursting or flaring sources. The EUSO-SPB2 flight was aborted after ~36h due to a leak in the balloon, resulting in a loss of the payload in the Pacific Ocean. During its descent, there was a loss of control over the payload rotation, interrupting plans for targeted ToO observations. However, there were some sources that crossed the CT's field of view during the descent of the balloon. These chance-coincident observations allow us to demonstrate the viability of conducting ToO follow-up observations from a near space environment, which could ultimately result in flux limits on associated astrophysical neutrino source candidates.