# Temporal Evolution of the Gamma-ray Burst Afterglow Spectrum for an Observer: GeV--TeV Synchrotron Self-Compton Light Curve

## TL;DR

This paper presents a numerical simulation of gamma-ray burst afterglow emission, revealing earlier onset times and smoother light curves than previous models, with implications for understanding high-energy photon detections.

## Contribution

The study introduces a comprehensive time-dependent simulation method for GRB afterglows, improving accuracy over analytical models and explaining observed high-energy photon features.

## Key findings

- Earlier afterglow onset time than analytical estimates
- Gamma-ray light curves can be smooth power-laws despite emission mechanism switching
- Discussion on model parameter uncertainties and spectral-decay relations

## Abstract

We numerically simulate the gamma-ray burst (GRB) afterglow emission with a one-zone time-dependent code. The temporal evolutions of the decelerating shocked shell and energy distributions of electrons and photons are consistently calculated. The photon spectrum and light curves for an observer are obtained taking into account the relativistic propagation of the shocked shell and the curvature of the emission surface. We find that the onset time of the afterglow is significantly earlier than the previous analytical estimate. The analytical formulae of the shock propagation and light curve for the radiative case are also different from our results. Our results show that even if the emission mechanism is switching from synchrotron to synchrotron self-Compton, the gamma-ray light curves can be a smooth power-law, which agrees with the observed light curve and the late detection of a 32 GeV photon in GRB 130427A. The uncertainty of the model parameters obtained with the analytical formula is discussed, especially in connection with the closure relation between spectral index and decay index.