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

Tobias Heibges, Claire Guépin, Diksha Garg, Luke Kupari, Mary Hall Reno, Tonia M. Venters, Lawrence Wiencke

TL;DR

This work demonstrates the feasibility of conducting Target-of-Opportunity searches for very-high-energy neutrino sources from a near-space Cherenkov telescope aboard EUSO-SPB2, including the development of the NuTS scheduling tool and a simulation chain that combines NuSpaceSim and EASCherSim with detector modeling. Although no neutrino events were observed during the shortened flight, the analysis establishes a concrete methodology for selecting candidate sources, simulating detector response, and computing all-flavor upper limits under best-case timing and realistic cloud conditions. The results quantify how environmental factors (e.g., clouds) and limited observation time impact sensitivity, and provide horizon-distance estimates for competing neutrino production models, informing design and planning for future missions such as POEMMA-Balloon with Radio. Overall, the paper validates the viability of ToO follow-ups from a near-space environment and outlines a scalable framework applicable to upcoming balloon- and space-based Cherenkov observatories.

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.

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

TL;DR

This work demonstrates the feasibility of conducting Target-of-Opportunity searches for very-high-energy neutrino sources from a near-space Cherenkov telescope aboard EUSO-SPB2, including the development of the NuTS scheduling tool and a simulation chain that combines NuSpaceSim and EASCherSim with detector modeling. Although no neutrino events were observed during the shortened flight, the analysis establishes a concrete methodology for selecting candidate sources, simulating detector response, and computing all-flavor upper limits under best-case timing and realistic cloud conditions. The results quantify how environmental factors (e.g., clouds) and limited observation time impact sensitivity, and provide horizon-distance estimates for competing neutrino production models, informing design and planning for future missions such as POEMMA-Balloon with Radio. Overall, the paper validates the viability of ToO follow-ups from a near-space environment and outlines a scalable framework applicable to upcoming balloon- and space-based Cherenkov observatories.

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 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 (). 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.

Paper Structure

This paper contains 8 sections, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Cherenkov telescope on EUSO-SPB2
  3. Neutrino Target Scheduler (NuTS) software
  4. Target of Opportunity Follow-up Searches
  5. Source selection
  6. Simulation criteria
  7. Upper limits and comparison to models
  8. Conclusion

Figures (2)

  • Figure 1: Skymap of observable sources during night 2. White stars indicate all sources that could have been observed. Colored stars are sources that crossed the CT's FoV, and are identified in the legend. The background color scale is a measure of the maximum observation time for observable regions of the sky (more detail in the text).
  • Figure 2: Calculated EUSO-SPB2 best-case upper limits on the neutrino fluence from GRB 230510A, assuming that the VHE neutrino burst occurred while the source was crossing the CT’s FoV. We show upper limits assuming no clouds (red) and accounting for clouds at $12$ km (blue). For comparison, we show GRB fluence models from Murase:2007yt, placing the source at a distance of $1$ Mpc (blue and orange lines). For reference, the 90% confidence upper limits from IceCube (green) and PAO (orange) in a $\pm$500 s window around the gravitational wave event from GW170817 adapted from Ackermann:2022rqc are shown.