Signatures of Recent Cosmic-Ray Acceleration in the High-latitude Gamma-Ray Sky

Journal Article · 11 August 2021 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ac01c9 · OSTI ID:1819497

Jóhannesson, Guđlaugur  ^[1]; Porter, Troy A.  ^[2]

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1. Univ. of Iceland, Reykjavik (Iceland). Science Inst.; KTH Royal Inst. of Technology, Stockholm (Sweden); Stockholm Univ. (Sweden)
2. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics & Cosmology, W.W. Hansen Experimental Physics Lab.

Cosmic-ray (CR) sources temporarily enhance the relativistic particle density in their vicinity over the background distribution accumulated from the Galaxy-wide past injection activity and propagation. If individual sources are close enough to the solar system, their localized enhancements may present as features in the measured spectra of the CRs and in the associated secondary electromagnetic emissions. Large-scale loop-like structures visible in the radio sky are possible signatures of such nearby CR sources. If so, these loops may also have counterparts in the high-latitude γ-ray sky. Using ~10 yr of data from the Fermi Large Area Telescope, applying Bayesian analysis including Gaussian Processes, we search for extended enhanced emission associated with putative nearby CR sources in the energy range from 1 GeV to 1 TeV for the sky region |b| > 30°. We carefully control the systematic uncertainty due to imperfect knowledge of the interstellar gas distribution. Radio Loop IV is identified for the first time as a γ-ray emitter, and we also find significant emission from Loop I. Furthermore, strong evidence is found for asymmetric features about the Galactic l = 0° meridian that may be associated with parts of the so-called "Fermi Bubbles," and some evidence is also found for γ-ray emission from other radio loops. Implications for the CRs producing the features and possible locations of the sources of the emissions are discussed.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: National Aeronautic and Space Administration (NASA); USDOE
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1819497
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 917; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English