Search for UHE neutrinos from GRBs with the Pierre Auger Observatory

TL;DR

This work targets the prompt UHE neutrino emission from GRBs using Phase I data from the Pierre Auger Observatory, leveraging NeuCosmA to generate GRB-specific neutrino fluences under multiple emission scenarios. By stacking the non-detections across hundreds of GRBs in Auger's neutrino-sensitive FoV and accounting for uncertainties in redshift, variability, and jet properties, the study places the strongest constraints to date on prompt GRB neutrino fluence above $10^{18}$ eV, complementing IceCube and ANTARES. The analysis demonstrates that Auger’s limits are particularly powerful at ultra-high energies, while different GRB models yield varying degrees of constraint, with ICMART being most constrained due to higher predicted fluxes. The results impact multimessenger constraints on GRB hadronic content and baryonic loading, informing models of UHECR origins and GRB jet physics.

Abstract

We report on the search for ultra-high-energy neutrinos from the prompt emission of gamma-ray bursts (GRBs) using Surface Detector (SD) data from Phase I of the Pierre Auger Observatory (2004-2021). A total of 570 GRBs occur within the most neutrino-sensitive field of view of the SD, considering both Earth-skimming and downward-going detection channels. For this purpose, GRB neutrino emission has been modeled using the numerical software NeuCosmA, incorporating gamma-ray measurements and inferred parameters such as the jet Lorentz factor and the minimum variability time scale. No neutrino candidates were found, and upper limits were obtained by stacking the individual GRB neutrino fluences. These limits are complementary to those of IceCube and ANTARES and provide the strongest constraints on prompt GRB neutrino fluence above $10^{18}$ eV. Additionally, limits on GRB fluence in alternative models of neutrino production have been derived using Auger data.

Figures (5)

• Figure 1: The predicted Waxman-Bahcall (WB) neutrino fluence for an individual GRB WaxBah, compared to the fluence obtained for an average GRB with the NeuCosmA numerical code (blue line). The yellow region indicates the energy range where the Pierre Auger Observatory is sensitive to showers induced by neutrinos.
• Figure 2: Redshift $z$ (left) and minimum variability timescale $t_v$ (right) distributions for all GRBs with available data. Red for short GRBs and blue for long GRBs. The thick lines correspond to the estimated PDFs (see text).
• Figure 3: Solid lines: Quasi-diffuse all-flavor neutrino flux (left-hand axis) and average fluence per GRB (right-hand axis) expected from the prompt phase of GRBs obtained with NeuCosmA for the sample of GRBs in the FoV of the Pierre Auger Observatory (this work, black line) and ANTARES Antares_Zegarelli (blue). Dashed lines represent the corresponding stacking limits $\Phi$ in Eq. \ref{['eq:Stack_flux']} and $\mathcal{F}_{\rm stack}$ in Eq. \ref{['eq:Stack_fluence']} at $90\%$ CL. The vertical scale shown inside the plot indicates the baryonic loading $f_p$ with $f_p=10$ assumed by default. In green, the expected neutrino emission (solid) and corresponding stacking limit (dashes) reported by IceCube for an IS Model IceCube, assuming average values of $\Gamma=300$ and $f_p=10$ for all GRB in the sample.
• Figure 4: Solid lines: Predicted quasi-diffuse all-flavor neutrino flux (left-hand axis) and average fluence per GRB (right-hand axis) for the photospheric (green), IS (blue) and ICMART (red) models with nuclear cascade, and $\Gamma = 300$, $z = 2$ and $f_A=10$ except for ICMART, $f_A=1$, and IS with NeuCosmA (no nuclear cascade, black). Dashed lines: corresponding stacking limits $\Phi$ in Eq. \ref{['eq:Stack_flux']} and $\mathcal{F}_{\rm stack}$ in Eq. \ref{['eq:Stack_fluence']} at $90\%$ CL. Limits to a flux $\propto E_\nu^{-4}$, as expected in the WB model, are also shown (gray).
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