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

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.

Accepted for publication in The Astrophysical Journal

References in corpus (10)

• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
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• Fermi LAT Observation of Supernova Remnant HB9
• Spectral and morphological study of the gamma radiation of the middle-aged supernova remnant HB 21
• Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources
• Fermi Large Area Telescope Observations of the Monoceros Loop Supernova Remnant
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• Multi-wavelength study of the galactic PeVatron candidate LHAASO J2108+5157
• Multi-Component Imaging of the Fermi Gamma-ray Sky in the Spatio-spectral Domain
• Probing cosmic ray escape from η Carinae
• Detection of very-high-energy gamma-ray emission from Eta Carinae during its 2020 periastron passage
• Exploring the nature of Galactic unassociated sources detected by the Fermi-LAT