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Scheduling follow-up observations of energetic transients with the neutrino target scheduler (NuTS)

This paper introduces the Neutrino Target Scheduler (NuTS), a flexible software tool designed to optimize follow-up observations of energetic transients for stratospheric balloon missions like the upcoming POEMMA Balloon with Radio, by integrating alert aggregation, observability analysis, and scheduling prioritization to detect ultra-high-energy neutrinos.

Original authors: Tobias Heibges, Claire Guépin, Luke Kupari, Hannah Wistrand, Randy Lahm, Johannes Eser, Mary Hall Reno, Tonia M. Venters, Lawrence Wiencke

Published 2026-08-05

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CC BY 4.0

Original authors: Tobias Heibges, Claire Guépin, Luke Kupari, Hannah Wistrand, Randy Lahm, Johannes Eser, Mary Hall Reno, Tonia M. Venters, Lawrence Wiencke

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe as a cosmic detective story, but instead of finding fingerprints, scientists are hunting for the most energetic particles in existence: ultra-high-energy cosmic rays and neutrinos. These are like ghostly messengers from the most violent events in the cosmos, such as exploding stars or black holes eating nearby stars. The problem is, these particles are incredibly rare and hard to catch. To solve the mystery of where they come from, astronomers use a "multi-messenger" approach. This means they don't just look for the particles; they also listen for gravitational waves and watch for flashes of light across the entire spectrum, from radio waves to gamma rays. When a telescope spots a sudden, energetic event—a "transient"—like a star being torn apart, it's a huge clue. If a neutrino detector can catch a particle from that same event at the same time, it's like finding the smoking gun. However, the universe is vast, and these events happen quickly. The challenge is figuring out exactly where to point a telescope, and when, to catch a glimpse of these fleeting cosmic fireworks before they disappear.

This paper introduces a new digital tool called the "Neutrino Target Scheduler," or NuTS, designed to solve this timing and pointing puzzle for high-altitude balloon missions. Think of NuTS as a super-smart, automated air traffic controller for a telescope floating in the stratosphere. The telescope, riding on a giant balloon, has a limited field of view and can only look in certain directions, especially when trying to spot neutrinos coming from below the Earth's curve. The balloon is also at the mercy of the wind, drifting along unpredictable paths, and the telescope can't look when the Sun or Moon is too bright.

The authors built NuTS to act as a three-part brain for the mission. First, the "Listener" module acts like a news aggregator, constantly scanning the internet for breaking alerts from global networks about new cosmic explosions. Second, the "Observability" module acts like a weather and geography expert; it takes the balloon's predicted path and the telescope's physical limits to calculate exactly which parts of the sky are visible and dark enough to see anything. Finally, the "Scheduler" module acts like a strategic game planner. It looks at the list of visible targets and decides which ones to chase first, based on how promising they are and how long the telescope can stare at them.

The paper demonstrates that this software works by running simulations using real flight data from a previous balloon mission and a mock database of alerts. The results show that NuTS can successfully filter out the noise, identify the best targets, and create a detailed flight plan for the telescope. For instance, the software can handle complex scenarios, like gravitational wave events that aren't pinpointed to a single spot but cover a huge area of the sky, by calculating the best angle to point the telescope to cover the most probable area. The authors show that with this tool, a mission can schedule observations for dozens of potential targets, prioritizing the most exciting ones like tidal disruption events or binary neutron star mergers. While the paper doesn't claim to have found a new neutrino yet, it proves that the software is ready to help the upcoming POEMMA-Balloon mission in 2028 make the most of its time in the sky, turning a drifting balloon into a precise, opportunistic hunter of the universe's most energetic secrets.

Technical Summary: Scheduling Follow-up Observations of Energetic Transients with the Neutrino Target Scheduler (NuTS)

Problem Statement
The detection of ultra-high-energy (UHE) neutrinos associated with transient astrophysical sources (e.g., blazar flares, tidal disruption events, gamma-ray bursts) is critical for identifying the origins of UHE cosmic rays. However, observing these elusive signals requires rapid, coordinated follow-up observations by instruments capable of slewing to transient sources. Existing astronomical scheduling tools (e.g., astroplan, SCOPES) are primarily designed for ground-based observatories and lack the specific capabilities required for moving detectors, such as stratospheric balloons. These tools do not adequately address the unique constraints of balloon-borne missions, including highly variable flight trajectories driven by wind patterns, specific field-of-view (FOV) geometries relative to the Earth's limb, and strict illumination constraints (Sun/Moon) required for optical Cherenkov detection. There is a need for a flexible, open-source software tool to optimize observation strategies for these specific conditions.

Methodology
To address these challenges, the authors developed the Neutrino Target Scheduler (NuTS), a modular Python package designed to integrate alert systems with detector trajectory data to generate optimized observation schedules. The software is structured around three primary modules:

Listener Module: This component interfaces with external alert networks, specifically the Gamma-ray Coordinates Network (GCN), the Transient Name Server (TNS), and Astronomer's Telegrams (ATels). It filters incoming alerts based on user-defined criteria (source type, detection time) to construct a comprehensive database of energetic transient sources. It also incorporates a database of steady sources (e.g., blazars, starburst galaxies) known to be potential VHE neutrino emitters. The module handles machine-readable alerts in real-time and processes non-machine-readable ATels manually or via user input.
Observability Module: This module convolves the source database with the specific properties of the detection system and the mission trajectory. It calculates which sources are observable within a given time window by considering:
- Trajectory: Interpolated balloon position data (latitude, longitude, altitude) and detector orientation.
- Field of View: The detector's azimuthal and altitudinal extents, specifically optimized for searching below the Earth's limb for neutrino-induced air showers.
- Illumination Constraints: Exclusion criteria based on Sun and Moon positions and illumination levels to ensure dark sky conditions necessary for Cherenkov light detection.
- Poorly Localized Sources: For events like gravitational wave (GW) candidates with large localization regions (HEALPix maps), the algorithm down-samples the sky map, treats pixels as point sources, and computes a "weighted time" metric ( $t_w = \sum p_i \Delta t_i$ ) to identify the optimal azimuthal pointing that maximizes the overlap between the detector's FOV and the probability region.
Scheduler Module: This module prioritizes the list of observable sources and generates a concrete observation schedule. It employs prioritization strategies based on:
- Source Type: A hierarchy ranking sources by their potential to produce detectable VHE neutrinos (e.g., Galactic supernovae and BNS mergers are highest priority, followed by flaring blazars and TDEs).
- Observation Time: Favoring sources that offer longer continuous observation windows within the mission constraints.
- Previous History: Prioritizing sources observed in previous windows to maximize total exposure.
  The scheduler accounts for operational constraints, such as the time required for telescope slewing (re-pointing) and minimum observation durations, to produce a feasible sequence of observations.

Key Contributions

Development of NuTS: The creation of a specialized, open-source software tool tailored for stratospheric balloon missions (specifically EUSO-SPB2 and the upcoming POEMMA-Balloon with Radio) that addresses the unique challenges of moving detectors and limb-pointing observations.
Modular Architecture: A design allowing independent execution of listening, observability calculation, and scheduling, facilitating flexibility for different mission phases and detector configurations.
Handling of Poorly Localized Sources: A specific algorithmic approach for scheduling follow-ups of GW events, optimizing telescope pointing to maximize the integration of probability regions within a limited FOV and slew time.
Integration with Simulation: The software is designed to interface with the $\nu$ SpaceSim simulation chain, allowing for the generation of source trajectories and observation schedules that can be directly used for sensitivity calculations.

Results
The authors validated NuTS using data from the SuperBit balloon mission (2023) and mock source databases derived from GCN, TNS, and ATels alerts.

Performance: The software demonstrates rapid execution times, with the observability module taking 1–5 seconds and the scheduler 1–15 seconds for point-source catalogs. For large GW localization regions (e.g., S190425z), runtimes increase to approximately 11 minutes due to the higher number of pixels processed.
Scheduling Efficiency: In mock campaigns simulating the SuperBit flight path, the software successfully identified observation windows constrained by Sun and Moon illumination, noting that only ~23% of the total flight time was available for observations.
Strategy Comparison: The authors compared two scheduling strategies: one prioritizing a wide variety of source types (Strategy 3) and one prioritizing repeated observations of previously scheduled sources (Strategy 4). The results showed that while Strategy 3 covered a broader range of source classes, Strategy 4 significantly increased the cumulative observation time for specific high-priority targets.
Visualization: The software generates various visualizations, including sky maps of observability, weighted-time profiles for GW events, and source trajectories relative to the detector FOV, aiding in the diagnostic analysis of scheduling decisions.

Significance and Claims
The paper claims that NuTS provides an essential capability for maximizing the scientific return of stratospheric balloon missions targeting VHE neutrinos. By automating the complex process of translating transient alerts into feasible observation schedules under strict geometric and illumination constraints, NuTS enables the first-time detection of UHE neutrinos from transient sources. The authors state that the initial release is tailored for the EUSO-SPB2 and the upcoming 2028 POEMMA-Balloon with Radio (PBR) missions. They emphasize that the software's modular nature allows for future adaptation to satellite missions (e.g., POEMMA) and ground-based detectors, facilitating precise comparisons between different detection techniques for VHE neutrino searches. The work represents a step toward optimizing multi-messenger follow-up strategies in the era of high-energy transient astronomy.

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