Klein-Nishina Corrections to the Spectra and Light Curves of Gamma-ray Burst Afterglows

TL;DR

This paper introduces a method and a Python tool for incorporating Klein-Nishina corrections into synchrotron and SSC models of GRB afterglows, improving the interpretation of their spectra and light curves.

Contribution

It provides a comprehensive framework and publicly available code for applying Klein-Nishina corrections to GRB afterglow modeling, enhancing spectral analysis accuracy.

Findings

Klein-Nishina corrections can explain harder X-ray spectra in GRB afterglows.

The spectral shapes are divided into multiple sub-regimes with distinct observational features.

The tool facilitates more accurate multi-wavelength modeling of relativistic transients.

Abstract

Multi-wavelength modeling of the synchrotron radiation from relativistic transients such as Gamma-ray Burst (GRB) afterglows is a powerful means of exploring the physics of relativistic shocks and of deriving properties of the explosion, such as the kinetic energy of the associated relativistic outflows. Capturing the location and evolution of the synchrotron cooling break is critical to break parameter degeneracies associated with such modeling. However, the shape of the spectrum above the cooling break, as well as the location and evolution of the break itself can be significantly altered by synchrotron self-Compton (SSC) cooling. We present an observer's guide to applying SSC cooling with and without Klein-Nishina (KN) corrections to GRB afterglow modeling. We provide a publicly available python code to calculate the Compton $Y$-parameter as a function of electron Lorentz factor, from which we compute changes to the electron distribution, along with KN-corrected afterglow spectra and light curves. In this framework, the canonical synchrotron spectral shapes split into multiple sub-regimes. We summarize each new spectral shape and describe its observational significance. We discuss how KN corrections can account for harder spectra and shallower decline rates observed in some GRB X-ray afterglows. Our overall aim is to provide an easy application of SSC+KN corrections into analytical multi-wavelength modeling frameworks for relativistic transients.