Searching for galactic cosmic ray pevatrons with multi-TeV gamma rays and neutrinos

TL;DR

This paper explores how supernova remnants can accelerate cosmic rays to PeV energies, producing detectable multi-TeV gamma rays and neutrinos, and discusses conditions for observing these signals to identify PeVatrons.

Contribution

It presents a model linking supernova remnant evolution to the production of multi-TeV gamma rays and neutrinos, proposing observational strategies for identifying cosmic PeVatrons.

Findings

Supernova remnants can accelerate particles to PeV energies during specific evolutionary phases.

Delayed gamma-ray and neutrino emissions can occur when energetic particles reach nearby gas clouds.

Detection of these signals can serve as indirect evidence of supernova remnants as PeVatrons.

Abstract

The recent HESS detections of supernova remnant shells in TeV gamma-rays confirm the theoretical predictions that supernova remnants can operate as powerful cosmic ray accelerators. If these objects are responsible for the bulk of galactic cosmic rays, then they should accelerate protons and nuclei to 10^15 eV and beyond, i.e. act as cosmic PeVatrons. The model of diffusive shock acceleration allows, under certain conditions, acceleration of particles to such high energies and their gradual injection into the interstellar medium, mainly during the Sedov phase of the remnant evolution. The most energetic particles are released first, while particles of lower energies are more effectively confined in the shell, and are released at later epochs. Thus the spectrum of nonthermal paticles inside the shell extends to PeV energies only during a relatively short period of the evolution of the remnant. For this reason one may expect spectra of secondary gamma-rays and neutrinos extending to energies beyond 10 TeV only from T \lesssim 1000 yr old supernova remnants. On the other hand, if by a chance a massive gas cloud appears in the \lesssim 100 pc vicinity of the supernova remnant, ``delayed'' multi-TeV signals of gamma-rays and neutrinos arise when the most energetic partices emerged from the supernova shell reach the cloud. The detection of such delayed emission of multi-TeV gamma-rays and neutrinos allows indirect identification of the supernova remnant as a particle PeVatron.