Search for new cosmic-ray acceleration sites within the 4FGL catalog Galactic plane sources

TL;DR

This study systematically searches for low-energy spectral breaks in gamma-ray sources near the Galactic plane using 8 years of Fermi LAT data, identifying potential new cosmic-ray acceleration sites including supernova remnants and binary systems.

Contribution

It provides the first comprehensive catalog of spectral breaks in 4FGL sources near the Galactic plane, expanding the list of potential cosmic-ray accelerators.

Findings

Identified 56 sources with confirmed spectral breaks.

Detected spectral features in 13 supernova remnants and other astrophysical objects.

Enhanced understanding of gamma-ray emission origins in the Galactic plane.

Abstract

Cosmic rays are mostly composed of protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions which in turn decay into gamma rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum, with a low-energy break around 200 MeV, was detected in the gamma-ray spectra of four Supernova Remnants (SNRs), IC 443, W44, W49B and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs. Here, we present a comprehensive search for low-energy spectral breaks among 311 4FGL catalog sources located within 5 degrees from the Galactic plane. Using 8 years of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV, we find and present the spectral characteristics of 56 sources with a spectral break confirmed by a thorough study of systematic uncertainty. Our population of sources includes 13 SNRs for which the proton-proton interaction is enhanced by the dense target material; the high-mass gamma-ray binary LS~I +61 303; the colliding wind binary eta Carinae; and the Cygnus star-forming region. This analysis better constrains the origin of the gamma-ray emission and enlarges our view to potential new cosmic-ray acceleration sites.