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Title: Seven-year Collection of Well-monitored Fermi -LAT Gamma-Ray Burst Afterglows

Here we present the light curves and spectra of 24 afterglows that have been monitored by Fermi-LAT at 0.1–100 GeV over more than a decade. All light curves (except 130427) are consistent with a single power law starting from their peaks, which occur in most cases before the burst end. The light curves display a brightness–decay rate correlation, with all but one (130427) of the bright afterglows decaying faster than the dimmer afterglows. We attribute this dichotomy to the quick deposition of relativistic ejecta energy in the external shock for the brighter/faster-decaying afterglows and to an extended energy injection in the afterglow shock for the dimmer/slower-decaying light curves. The spectra of six afterglows (090328, 100414, 110721, 110731, 130427, 140619B) indicate the existence of a harder component above a spectral dip or ankle at energies of 0.3–3 GeV, offering evidence for inverse-Compton emission at higher energies and suggesting that the harder power-law spectra of five other LAT afterglows (130327B, 131231, 150523, 150627, 160509) could also be inverse-Compton, while the remaining, softer LAT afterglows should be synchrotron emission. Finally, marginal evidence for a spectral break and softening at higher energies is found for two afterglows (090902B and 090926).
Authors:
ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-16-23641
Journal ID: ISSN 1538-4357; TRN: US1700681
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 837; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE; National Aeronautic and Space Administration (NASA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Astronomy and Astrophysics
OSTI Identifier:
1351224