http://arxiv.org/abs/1605.09367
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 in time. All light-curves 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 a quick deposition of the relativistic ejecta energy in the external-shock for the former type and to an extended energy-injection in the afterglow shock for the latter. The spectra of 10 afterglows are better described with a broken power-law than a single power-law, indicating the existence of a hard component above a dip energy that ranges from 0.5 GeV to 5 GeV, and at a 1-3 sigma confidence level. We interpret those spectra as being synchrotron self-Compton emissions, and suggest that power-law photon spectra softer than dN/dE ~ E^{-2} are synchrotron, while those harder than that are inverse-Compton. Marginal evidence for a spectral softening is found for two afterglows.
A. Panaitescu
Tue, 31 May 16
27/70
Comments: 12 pages
You must be logged in to post a comment.