Multi-Messenger High-Energy Results

TL;DR

Multi-messenger high-energy astrophysics combines neutrino, gamma-ray, and gravitational wave observations to uncover cosmic ray origins, source mechanisms, and the role of different astrophysical objects, with recent discoveries highlighting neutrino sources and multimessenger correlations.

Contribution

This paper reviews recent advances in multi-messenger high-energy astrophysics, emphasizing new neutrino detections, source identifications, and the integration of multimessenger data for cosmic ray studies.

Findings

IceCube detected a diffuse flux of high-energy neutrinos above 60 TeV.

First strong evidence of a standalone neutrino source.

Coincidence of neutrino alerts with gamma-ray observations.

Abstract

Multi-messenger high-energy astrophysics has currently achieved the potential to unravel the origin of cosmic rays and how sources accelerate them, their relation to the diffuse radiation in the extra-galactic space, and their role to forge their galaxies of origin while they wander in their magnetic fields for millions of years. Neutrino astronomy produced its major scientific milestone with the discovery by IceCube of a diffuse flux at energies above 60~TeV with intensity comparable to a predicted upper limit to the flux from extra-galactic sources of ultra-high energy cosmic rays. More recent results provide the first strong evidence of a standalone neutrino source and a highly probable coincidence of a neutrino alert with gamma rays. These results of IceCube indicate that neutrino astronomy can complement photon astronomy also providing insights into opaque sources of high-energy radiation. Starburst galaxies and jetted black holes in active galaxies are favored candidates to explain the diffuse cosmic neutrino background. Additionally, gamma-ray bursts remain an intriguing mystery now enriched by joint observations of gamma-rays and gravitational waves. The galactic diffuse flux, produced by cosmic ray interactions on the interstellar matter of our galaxy and peaking at lower energies, is within the reach of neutrino detectors. Together with the measured galactic gamma-ray flux up to PeV energies, they will shed light on the knee region of cosmic rays and the possible existence of dark matter in the Galactic plane. In the future, more work will be done in IceCube and deep sea and lake neutrino telescopes to use further low-energy cascades for cosmic source searches thanks to improved descriptions of detection media and deep learning methods.