Detecting Neutrino Emission from Supernova Remnants: A Theoretically Motivated Target Catalog

Abstract

Galactic supernova remnants (SNRs) are thought to accelerate cosmic rays (CRs) to several PeV energies, but this has yet to be confirmed as general behavior. Although several sources show ~100 TeV gamma rays, their hadronic origin is uncertain; a matching neutrino signal would provide definitive evidence. Using insight from the theory of diffusive shock acceleration, we evaluate the spectra and environments of the sample of Galactic SNRs to identify those most likely to be hadronic, categorizing them into a tiered catalog depending on their likelihood to produce neutrinos detectable in the TeV-PeV range. We then calculate the estimated stacked sensitivity of IceCube for each tier using IceCube's ten-year public data. Our results suggest that this strategy of stacking SNRs and carefully excluding leptonic sources by using theoretical arguments may allow for a detection of this source class that would otherwise be impossible. A follow-up analysis of these catalogs using TeV-PeV sensitive neutrino data from IceCube (or similar telescopes like KM3NeT/ARCA) offers the most decisive, near-future test for the hadronic nature of these SNRs and the maximum energies of their CR spectra.

Figures (8)

• Figure 1: The relative positions of known Galactic SNRs from Green25(green points), and the selected subset of SNRs in our Tier 1, 2, and 3 catalogs (magenta, cyan, and white points respectively). Source for background image: Gaia [ESA/Gaia/DPAC, Stefan Payne-Wardenaar] GaiaMilkyWayMap2025. Distances are approximate and are taken from Green25 when available, and otherwise from Ranasinghe+24 and Wang+20 to reach complete coverage for all SNRs.
• Figure 2: Flowchart of our classification procedure to sort SNRs into Tiers 1, 2, or 3, or to exclude them from all tiers. Steep spectra are defined as those with spectral indices $q>2.1$. Beneath each tier is the tier-dependent analysis strategy for evaluating the neutrino contribution of the contained sample of SNRs, where PL stands for power law, either with or without an exponential cutoff as noted.
• Figure 3: Spectral fits of representative SNRs from each Tier of our catalog: W51C (Tier 1, purple) has a steep spectrum and observed emission at energies above a TeV; W44 (Tier 2, blue) has a steep slope but has not been observed above a TeV; MGRO J1908+06 (Tier 2, orange) has a concave spectrum where the low-energy portion may be hadronic and may extend subdominantly to TeV energies (orange dotted line); Vela Jr (Tier 3, green) has a hard spectral index but is very bright at TeV energies.
• Figure 4: Spectral fits for all sources in the Tier 1 catalog assuming power laws with exponential cutoffs.
• Figure 5: Spectral fits for all Tier 2 sources assuming power-law spectra with no cutoffs.