Chasing Serendipity: Tackling Transient Sources with Neutrino Telescopes

TL;DR

The paper develops a framework to incorporate right ascension into the effective area of neutrino telescopes, enabling realistic searches for transient point sources with non-polar detectors. By mapping equatorial coordinates to local detector coordinates and accounting for Earth attenuation, the authors demonstrate RA-dependent sensitivities across a global network and apply the method to evaporating primordial black holes as a case study. They show that detector sensitivity, localization, and complementarity with gamma-ray observatories depend strongly on the source position and time, justifying coordinated multi-detector analyses. The results indicate that a four-detector network can triangulate PBH bursts and that gamma-ray and neutrino observations together expand sky coverage, with implications for constraining local PBH populations and multimessenger astrophysics.

Abstract

The discovery of ultra-high-energy neutrinos by IceCube marked the beginning of neutrino astronomy. Yet, the origin and production mechanisms of these neutrinos remain an open question. With the observation of several neutrino events with energies about the PeV, transient sources - astrophysical objects that emit particles in brief, localized bursts - have emerged as promising candidates. In this work, we revisit the identification of such sources in IceCube and future neutrino telescopes, focusing on how both the timing and sky localization of the source affect the detection sensitivity. We present a framework to account for the source's right ascension in determining the effective area of detectors not located at the poles, such as KM3NeT. As a case study, we investigate evaporating primordial black holes (PBHs) as transient neutrino sources, showing that the detection prospects and localization accuracy are strongly influenced by the PBH's position in the sky. Our results emphasize the complementarity between neutrino and gamma-ray observatories and showcase the potential of a global network of neutrino detectors to identify and localize transient events that might be missed by traditional photon-based instruments.

Figures (9)

• Figure 1: Illustration of the field of view in equatorial coordinates covered by existing gamma-ray experiments: HAWC historical:2023opoHAWC:2019wla (purple) and LHAASO DiSciascio:2016rgiLHAASO:2019qtb (light green), VERITAS VERITAS:2006lycArchambault:2017asc (orange), HESS HESS:2018pbpHESS:2023zzd (red), Telescope Array TelescopeArray:2012qquTelescopeArray:2012uws (cyan) and Pierre Auger PierreAuger:2015eyc (golden). We also include future experiments, represented by the hatched areas: SWGO (gray) SWGO:2025tajChiavassa:2025aym and CTA (light brown) CTA-SST-1Mproject:2021kqa. The colored regions denote the instantaneous field of view of these experiments on February 13th at 01:00:00 UTC, our benchmark date. The area encompassed by the dashed line represents the instantaneous field of view of the corresponding experiment one hour earlier with respect to the event. The gray line indicates the galactic plane.
• Figure 2: Relationship between source declination $\delta$ and the local zenith angle $\theta$ for IceCube (blue) and KM3NeT, assuming a fixed right ascension of $\text{RA} = 94.3^\circ$ on February 13th 01:00:00 UTC (solid orange) and ten hours later (dashed orange). We also highlight by the dotted gray line the value corresponding to $\delta=-7.8^\circ$.
• Figure 3: The top and middle left panels show the effective areas of IceCube and KM3NeT, respectively, on February 13th at 01:00:00 UTC. The bottom left panel shows the same information for KM3NeT, but evaluated ten hours later. The right panels displays the reconstructed neutrino trajectory through the Earth, shown in local coordinates for an event at $(\delta,\rm{RA}) =(-7.8^\circ, 94.3^\circ)$.
• Figure 4: Top: Portion of the sky in equatorial coordinates that is covered by gamma-ray detectors. The gray region denotes the region where a PBH could have been observed by gamma-ray experiments. The upper gray region is the one-day coverage by LHAASO and HAWC, while the region with the dashed contour is the instantaneous field of view of Pierre Auger for February 13th 01:00:00 UTC. The colored points indicate the location in the sky obtained by transforming the terrestrial coordinates the neutrino telescopes.
• Figure 5: The PBH instantaneous differential muon neutrino spectrum $d^2N_{\nu_\mu}/dEdt$ as a function of the energy. We show curves for $\tau_B =$ 1 day (blue), 10 s (yellow) and $10^{-9}$ s (red) before the PBH fully explodes. The dashed lines indicate the PBH temperature $T_{\text{PBH}}$ at the time $\tau_B$.