GRB afterglow parameters in the era of TeV observations: the case of GRB~190114C

Abstract

The afterglow of GRB~190114C has been observed at {60-1200~s} after the burst in the {sub-TeV range} by the {MAGIC Cherenkov} telescope. The simultaneous observations in X-ray range, which is presumed to be of synchrotron origin, and in sub-TeV range, where the emission is presumed to be inverse Compton, provide new stringent constraints on the conditions within the emitting regions {and their evolution in time}. While the additional data contain a lot of new information, it turns out that fitting both the X-ray and the TeV emission, is much more complicated than what was originally anticipated. We find that optical flux measurements provide important complementary information that in combination with TeV measurements breaks degeneracy in the parameter space. We present here a numerical fit to the multi-wavelength observed spectrum using a new code that calculates the single-zone synchrotron including self-Compton emission taking into account the exact Klein-Nishina cross-sections as well as pair production via absorption of the high-energy photons inside the emitting zone and the emission from the resulting secondary pairs. We also present a revised set of single zone parameters and a method for fitting the data to the observations. Our model for GRB~190114C that fits all the observations, from the optical data point to the sub-TeV range, suggests that it is in the fast cooling regime. The inferred parameters for observations {at two separate moments of time} show significant deviations from some of the common expectations in afterglow modeling but are all consistent with the predictions of the {pair-balance} model.