Gamma-ray burst afterglow broadband fitting based directly on hydrodynamics simulations

TL;DR

This paper introduces a new, efficient tool for fitting gamma-ray burst afterglow data using hydrodynamical simulations, enabling more accurate parameter estimation and modeling of jet features.

Contribution

The authors develop a fast, simulation-based fitting method that captures complex jet dynamics and features previously unmodeled analytically, improving afterglow data analysis.

Findings

Successful fit of GRB 990510 data across radio, X-ray, optical bands.

Revealed differences in explosion parameters compared to earlier studies.

Enhanced model fit when including observer angle.

Abstract

We present a powerful new tool for fitting broadband gamma-ray burst afterglow data, which can be used to determine the burst explosion parameters and the synchrotron radiation parameters. By making use of scale invariance between relativistic jets of different energies and different circumburst medium densities, and by capturing the output of high-resolution two-dimensional relativistic hydrodynamical (RHD) jet simulations in a concise summary, the jet dynamics are generated quickly. Our method calculates the full light curves and spectra using linear radiative transfer sufficiently fast to allow for a direct iterative fit of RHD simulations to the data. The fit properly accounts for jet features that so far have not been successfully modeled analytically, such as jet decollimation, inhomogeneity along the shock front and the transitory phase between the early time relativistic and late time non-relativistic outflow. As a first application of the model we simultaneously fit the radio, X-ray and optical data of GRB 990510. We not only find noticeable differences between our findings for the explosion and radiation parameters and those of earlier authors, but also an improved model fit when we include the observer angle in the data fit. The fit method will be made freely available on request and on-line at http://cosmo.nyu.edu/afterglowlibrary. In addition to data fitting, the software tools can also be used to quickly generate a light curve or spectrum for arbitrary observer position, jet and radiation parameters.