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

Abstract

Major Atmospheric Gamma Imaging Cherenkov 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 {\it Fermi}. This gives an interesting constraint on the acceleration efficiency for Weibel-mediated shocks. We also constrain the number fraction of non-thermal electrons $f_{\mathrm{e}}$, and the temperature of the thermal electrons. The early optical emission can be explained by the thermal synchrotron emission with $f_{\mathrm{e}}\lesssim 0.01$. On the other hand, the X-ray light curves restrict efficient energy transfer from protons to the thermal electrons, and $f_{\mathrm{e}}\sim 1$ is required if the energy fraction of the thermal electrons is larger than $\sim 10$\%. The parameter constraints obtained in this work give important clues to probing plasma physics with relativistic shocks.

9 pages, 10figures, ApJ in press

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