An Efficient Method for Fitting Radiation-mediated Shocks to Gamma-Ray Burst Data: The Kompaneets RMS Approximation

Shocks that occur below a gamma-ray burst (GRB) jet photosphere are mediated by radiation. Such radiation-mediated shocks (RMSs) could be responsible for shaping the prompt GRB emission. Although well studied theoretically, RMS models have not yet been fitted to data due computational cost of simulating RMSs from first principles. Here, we bridge gap between theory and observations developing an approximate method capable accurately reproducing radiation spectra mildly relativistic (in shock frame) or slower RMSs, called Kompaneets approximation (KRA). The is based on similarities thermal Comptonization bulk occurs inside RMS. We validate comparing simulated KRA first-principle radiation-hydrodynamics simulations, finding excellent agreement both in downstream. then applied scenario jet, allowing fast efficient fitting data. illustrate capabilities developed performing fit non-thermal spectrum 150314A. allows us uncover physical properties emission, such as speed upstream plasma temperature.