Year: 2020
Type: article
Abstract: Energy injection into the external shock system that generates the afterglow to a gamma-ray burst (GRB) can result in a rebrightening of the emission. Here we investigate the off-axis view of a rebrightened refreshed shock afterglow. We find that the afterglow light curve, when viewed from outside of the jet opening angle, could be characterized by a slow rise, or long plateau, with a maximum flux determined by the total system energy. Using the broadband afterglow data for GRB 170817A, associated with the gravitational-wave-detected binary neutron star merger GW170817, we show that a refreshed shock model with a simple top-hat jet can reproduce the observed afterglow features. We consider two refreshed shock models: a single episode of energy injection, and an episode of continuous energy injection. The best-fit model parameters give a jet opening angle for our first and second models, respectively, of θ j = 5.° and 6.° , an inclination to the line of sight ι = 16.° and 17.° , an initial on-axis isotropic equivalent kinetic energy and erg, and a total/final, on-axis isotropic equivalent refreshed shock energy and erg. The first model fitting prefers an initial bulk Lorentz factor Γ0,1 < 60, with a comparatively low central value of Γ0,1 = 19.5, indicating that, in this case, the on-axis jet could have been a “failed GRB.” Alternatively, our second model is consistent with a bright GRB for an on-axis observer, with . Due to the low Lorentz factor and/or the jet opening angles at θ j ∼ ι/3, both models are unable to reproduce the γ-ray emission observed in GRB 170817A, which would therefore require an alternative explanation such as cocoon shock breakout.
Source: The Astrophysical Journal
Authors: Gavin P. Lamb, Andrew J. Levan, Nial R. Tanvir
Institutions: University of Leicester, Radboud University Nijmegen
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: Rolling Grant Programme in Astrophysics, Planetary Science and Space Instrumentation - 2010-2015, Astrophysics Research at the University of Leicester, Rolling Grant Programme in Astrophysics, Planetary Science and Space Instrumentation - 2007-2012, Astrophysics Research at the University of Leicester
OpenAlex ID: W3029025367