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

TL;DR

This paper reports on the EUSO-SPB2 mission's Cherenkov Telescope search for very high energy neutrinos from astrophysical sources, introduces a new scheduling software, and discusses the potential of balloon-based ToO observations.

Contribution

It presents the first targeted search for VHE neutrinos using a Cherenkov Telescope onboard a near-space balloon and introduces the Neutrino Target Scheduler software tool.

Findings

Demonstrated the feasibility of ToO follow-up from near space.

Calculated upper limits on neutrino fluences from observed sources.

Showed potential for future balloon missions like POEMMA-Balloon.

Abstract

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission launched from Wanaka New Zealand on May 13, 2023. The mission ended after 36 h due to a balloon leak that resulted in the payload being lost in the Pacific Ocean. Over the course of the mission, the onboard Cherenkov Telescope (CT) was pointed just below the Earth's limb to search for optical signals from upward-moving extensive air showers that were induced by decaying tau-leptons that were generated by the conversion of $>10$ PeV tau-neutrinos in Earth. Such very-high energy (VHE) neutrinos may be produced in several classes of astrophysical sources that are suspected of possibly accelerating particles to ultra-high energies. In this contribution, we discuss the EUSO-SPB2 Target-of-Opportunity (ToO) campaign to search for VHE neutrino signals coming from astrophysical sources that crossed the CT's field of view ($6.4^\circ \times 12.8^\circ$). We also present a new software tool designed for scheduling observations, the Neutrino Target Scheduler, that we developed to support the ToO campaign. We also calculate upper limits on the neutrino fluences from sources observed during the ToO campaign. Our observations demonstrate the viability of conducting ToO follow-up observations from a near space environment with future balloon missions, such as the pathfinder mission POEMMA-Balloon with Radio.