Abstract
Very-high-energy (VHE; ≥ 10 GeV) photons are expected from the nearest and brightest gamma-ray bursts (GRBs). VHE photons, at energies higher than 300 GeV, were recently reported by the MAGIC Collaboration for this burst. Immediately, GRB 190114C was followed up by a massive observational campaign covering a large fraction of the electromagnetic spectrum. In this Letter, we obtain the Large Area Telescope (LAT) light curve of GRB 190114C and show that it exhibits similar features to other bright LAT-detected bursts; the first high-energy photon (≥100 MeV) is delayed with the onset of the prompt phase and the flux light curve exhibits a long-lasting emission (much longer than the prompt phase) and a short-lasting bright peak (located at the beginning of long-lasting emission). Analyzing the multi-wavelength observations, we show that the short-lasting LAT and Gamma-Ray Burst Monitor bright peaks are consistent with the synchrotron self-Compton reverse-shock model, and that the long-lasting observations are consistent with the standard synchrotron forward-shock model that evolves from a stratified stellar-wind-like medium to a uniform interstellar-medium-like medium. Given the best-fit values, a bright optical flash produced by synchrotron reverse-shock emission is expected. From our analysis we infer that the high-energy photons are produced in the deceleration phase of the outflow, and some additional processes to synchrotron in the forward shocks should be considered to properly describe the LAT photons with energies beyond the synchrotron limit. Moreover, we claim that an outflow endowed with magnetic fields could describe the polarization and properties exhibited in the light curve of GRB 190114C.