Detection of the Characteristic Pion-Decay Signature in Supernova Remnants

TL;DR

This paper reports the first detection of characteristic pion-decay gamma-ray signatures in supernova remnants, providing direct evidence that these remnants accelerate cosmic-ray protons.

Contribution

The study presents the first clear detection of pion-decay gamma rays in SNRs, confirming proton acceleration in these astrophysical objects.

Findings

Detection of pion-decay gamma rays in SNRs IC 443 and W44

Evidence supporting SNRs as sources of galactic cosmic-ray protons

Confirmation of proton acceleration through gamma-ray spectral analysis

Abstract

Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.