Are the missing X-ray breaks in Gamma-ray Burst afterglow light curves merely hidden?

TL;DR

This paper investigates whether the apparent lack of X-ray breaks in GRB afterglow light curves is due to these breaks being hidden, which could impact interpretations of jet properties and cosmological uses.

Contribution

It introduces a method to identify hidden X-ray breaks in GRB afterglow light curves using synthetic data and statistical analysis.

Findings

Hidden breaks can be misinterpreted as single power laws.

Caution is needed when concluding the absence of achromatic breaks.

Swift-era data may still conceal true jet breaks.

Abstract

Gamma-ray burst afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as cosmological tools. Here we address the issue of X-ray breaks that are possibly `hidden' and hence the light curves are misinterpreted as being single power laws. We do so by synthesising XRT light curves and fitting both single and broken power laws, and comparing the relative goodness of each fit via Monte Carlo analysis. Even with the well sampled light curves of the Swift era, these breaks may be left misidentified, hence caution is required when making definite statements on the absence of achromatic breaks.