Overview of the EUSO-SPB2 Target of Opportunity program using the Cherenkov Telescope

Abstract

During the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission, we planned Target of Opportunity (ToO) operations to follow up on possible sources of ≳ 10 PeV neutrinos. The original plan before flight was to point the onboard Cherenkov Telescope (CT) to catch the source's path on the sky just below Earth's horizon. By using the Earth as a tau-neutrino to tau-lepton converter, the CT would then be able to look for optical extensive air shower signals induced by tau-lepton decays in the atmosphere. The CT had a field of view of 6.4 • vertical × 12.8 • horizontal. Possible neutrino source candidates include gamma ray bursts, tidal disruption events and other bursting or flaring sources. In addition, follow-ups of binary neutron star mergers would have been possible after the start of the O4 observation run from LIGO-Virgo-KAGRA. The resulting exposure is modeled using the NuSpaceSim framework in ToO mode. With the launch of the EUSO-SPB2 payload on the 13th May 2023, this summarizes the ToO program status and preliminary data, as available.

Overview and First Results of EUSO-SPB2

“…4. A full machinery was developed to follow up on such alerts and to prioritize them to maximize the chances of neutrino observations (for details, see [16][17][18].…”

Neutrino Target-of-Opportunity Sky Coverage and Scheduler for EUSO-SPB2

“…Transient and steady source database: The first module of the ToO software is a listening module designed to filter alerts from various alert networks, such as the Gamma-ray Coordination Network (GCN) and the Transient Name Server (TNS). GCN and TNS alerts are available in machine-readable formats [12]. Several criteria determine which alerts are added to a source database: we select alerts corresponding to potential sources of VHE neutrinos.…”

“…Moreover, we develop a strategy to observe extended sources such as TA old/new hotspots [9,10] or localization probabilities from gravitational wave signals [11]. Further details on the ToO program and prioritizations of ToO neutrino sources appear in these proceedings [12,13]. A flowchart of the ToO software is shown in figure 1.…”

The Targets of Opportunity Source Catalog for the EUSO-SPB2 Mission

“…ToO observations are scheduled for each nightly period of possible CT operation based on the values included in their catalog entries. More information on this scheduling process can be found in [17,18].…”