Abstract
An overview about the multi-messenger capabilities of the Pierre Auger Observatory is presented. The techniques and performance of searching for Ultra-High Energy neutrinos, photons and neutrons are described. Some of the most relevant results are reviewed, such as stringent upper bounds that were placed to a flux of diffuse cosmogenic neutrinos and photons, bounds placed on neutrinos emitted from compact binary mergers that were detected by LIGO and Virgo during their first and second observing runs, as well as searches for high energy photons and neutrons from the galactic center that constrain the properties of the putative galactic PeVatron, observed by the H.E.S.S. collaboration. The observation of directional correlations between ultra-high energy cosmic rays and either high energy astrophysical neutrinos or specific source populations weighted by their electromagnetic radiation are also discussed. They constitute additional multi-messenger approaches aimed at identifying the sources of high energy cosmic rays.
Highlights
With the discovery of neutrinos from SN1987A (Bionta et al, 1987; Hirata et al, 1987) arriving 4 h before the light detected by conventional telescopes it became clear that there was a lot to learn from examining any type of particles and radiation coming from astrophysical objects, and that neutrino detectors could give early alerts that would facilitate the observation of the evolution of such transients from the earliest stages
To test these models against the observed Ultra-High Energy Cosmic Rays (UHECRs) sky maps, a maximum-likelihood analysis was performed with two free parameters aimed at maximizing the degree of correlations of the model maps with UHECR events: (a) the fraction of an isotropic component contributing to the total UHECR flux in addition to the source population being tested, and (b) the width of a 2D Gaussian smearing around the position of the source candidates
We have summarized a few prominent examples that demonstrate the unprecedented sensitivities to ultra-high energy (UHE) photons, neutrinos, and neutrons
Summary
With the discovery of neutrinos from SN1987A (Bionta et al, 1987; Hirata et al, 1987) arriving 4 h before the light detected by conventional telescopes it became clear that there was a lot to learn from examining any type of particles and radiation coming from astrophysical objects, and that neutrino detectors could give early alerts that would facilitate the observation of the evolution of such transients from the earliest stages. There is no known possibility to separate neutron-induced showers from the charged cosmic rays on the basis of the shower development but, since neutrons are directional, it is in principle possible to identify sources of nearby neutrons by looking at an excess from given directions or to exploit potential time and directional correlations. This procedure could be applied to any type of neutral particles that induce a shower in the atmosphere such as photons. We review the capability of the Observatory to search for signals of such particles and discuss the contributions that have been made
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