Synchrotron Self-Compton as a Likely Mechanism of Photons beyond the Synchrotron Limit in GRB 190114C

Abstract

GRB 190114C, a long and luminous burst, was detected by several satellites and ground-based telescopes from radio wavelengths to GeV gamma-rays. In the GeV gamma-rays, the Fermi Large Area Telescope detected 48 photons above 1 GeV during the first 100 s after the trigger time, and the MAGIC telescopes observed for more than 1000 s very high-energy (VHE) emission above 300 GeV. Previous analysis of the multi-wavelength observations showed that, although these are consistent with the synchrotron forward-shock model that evolves from a stratified stellar-wind to a homogeneous ISM-like medium, photons above a few GeV can hardly be interpreted in the synchrotron framework. In the context of the synchrotron forward-shock model, we derive the light curves and spectra of the synchrotron self-Compton (SSC) model in a stratified and homogeneous medium. In particular, we study the evolution of these light curves during the stratified-to-homogeneous afterglow transition. Using the best-fit parameters reported for GRB 190114C we interpret the photons beyond the synchrotron limit in the SSC framework and model its spectral energy distribution. We conclude that low-redshift gamma-ray bursts described under a favorable set of parameters as found in the early afterglow of GRB 190114C could be detected at hundreds of GeV, and also afterglow transitions would allow that VHE emission could be observed for longer periods.