Search for Spatial Correlations of Neutrinos with Ultra-high-energy Cosmic Rays

Abstract

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.

Constraints on Populations of Neutrino Sources from Searches in the Directions of IceCube Neutrino Alerts

“…This is done by calculating the local point source test statistic map and adding to it a logarithmic penalty term from the skymap. This procedure was initially developed in the context of searching for joint sources of ultra-high-energy cosmic rays and neutrinos (Albert et al 2022) and has been used to search for neutrinos coincident with ANITA events (Aartsen et al 2020e), gravitational waves (Aartsen et al 2020c), and gamma-ray bursts (Abbasi et al 2022b). We then repeat this followup procedure for every alert in our catalog and for each of the three timescales described above.…”

A nearby source of ultra-high energy cosmic rays

“…Those constraints were set for particles with deflections not larger than 30 • , which implies light or intermediate composition. Indeed, the deflection of 100 EeV proton in the galactic magnetic field is approximately 3 • , when estimated as a median over all directions in the sky in either JF12 or PT11 GMF model [27]. Thus, Auger result obtained for E > 80 EeV CRs should be attributed to the observed particles with Z ≲ 8.…”

High-Energy and Ultra-High-Energy Neutrino Astrophysics

“…The remaining part of the flux is, therefore, most likely extragalactic, with recent studies confirming that even the flavor composition is consistent with isotropy [44]. In order to identify its sources, the IceCube Collaboration adopts different strategies, including searches for multiplets of events from similar directions in the sky [9,[45][46][47][48], cross-correlation of neutrino angular distribution with catalogs of known sources [49][50][51][52][53][54][55][56][57][58][59][60][61][62] and with ultra-high-energy cosmic rays [63][64][65], the analysis of the neutrino angular power spectrum [66][67][68][69], and searches for temporal and spatial correlations with transient sources [70,71]. Up to now, the IceCube Collaboration has reported on the detection of two sources, the Seyfert galaxy NGC 1068 [10], and the blazar TXS 0506 + 056 [6,7].…”