Probing Particle Acceleration through Broadband Early Afterglow Emission of MAGIC Gamma-Ray Burst GRB 190114C

Major Atmospheric Gamma Imaging Cerenkov Telescopes (MAGIC) detected the gamma-ray afterglow of GRB 190114C, which can constrain microscopic parameters of the shock-heated plasma emitting non-thermal emission. Focusing on the early afterglow of this event, we numerically simulate the spectrum and multi-wavelength light curves with constant and wind-like circumstellar medium using a time-dependent code. Our results show that the electron acceleration timescale at the highest energies is likely shorter than 20 times the gyroperiod to reproduce the GeV gamma-ray flux and its spectral index reported by Fermi. This gives an interesting constraint on the acceleration efficiency for Weibel-mediated shocks. We also constrain the number fraction of non-thermal electrons f(e), and the temperature of the thermal electrons. The early optical emission can be explained by the thermal synchrotron emission with f(e) less than or similar to 0.01. On the other hand, the X-ray light curves restrict efficient energy transfer from protons to the thermal electrons, and f(e) similar to 1 is required if the energy fraction of the thermal electrons is larger than similar to 10%. The parameter constraints obtained in this work give important clues to probing plasma physics with relativistic shocks.