# Is Spectral Width a Reliable Measure of GRB Emission Physics?

## TL;DR

This paper critically evaluates the reliability of spectral width as a measure of GRB emission physics, demonstrating that physical model fitting provides a more accurate approach than width-based criteria.

## Contribution

It shows that spectral width alone is insufficient for physical inference and advocates for direct physical model fitting in GRB spectral analysis.

## Key findings

- Many spectra fit by synchrotron models despite width-based rejection.
- Previous width measures fail due to multiple widths and spectral curvature.
- Fitting physical models is more reliable than width-based criteria.

## Abstract

The spectral width and sharpness of unfolded, observed GRB spectra have been presented as a new tool to infer physical properties about GRB emission via spectral fitting of empirical models. Following the tradition of the 'line-of-death', the spectral width has been used to rule out synchrotron emission in a majority of GRBs. This claim is investigated via reexamination of previously reported width measures. Then, a sample of peak-flux GRB spectra are fit with an idealized, physical synchrotron model. It is found that many spectra can be adequately fit by this model even when the width measures would reject it. Thus, the results advocate for fitting a physical model to be the sole tool for testing that model. Finally, a smoothly-broken power law is fit to these spectra allowing for the spectral curvature to vary during the fitting process in order to understand why the previous width measures poorly predict the spectra. It is found that the failing of previous width measures is due to a combination of inferring physical parameters from unfolded spectra as well as the presence of multiple widths in the data beyond what the Band function can model.