The hidden X-ray breaks in afterglow light curves

TL;DR

This paper investigates the possibility that X-ray breaks in GRB afterglow light curves are often hidden, leading to misinterpretation of jet breaks and affecting our understanding of GRB physics and their use as standard candles.

Contribution

It demonstrates how hidden X-ray breaks can be identified through simulations and discusses methods for better detection using multi-wavelength analysis.

Findings

Hidden breaks exist in well-sampled light curves.

Monte Carlo simulations reveal trends in X-ray light curves.

Multi-wavelength analysis improves break detection.

Abstract

Gamma-Ray Burst (GRB) 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 standard candles. Here we address the issue of X-ray breaks which are possibly 'hidden' and hence the light curves are misinterpreted as being single power-laws. We show how a number of precedents, including GRB 990510 & GRB 060206, exist for such hidden breaks and how, even with the well sampled light curves of the Swift era, these breaks may be left misidentified. We do so by synthesising X-ray light curves and finding general trends via Monte Carlo analysis. Furthermore, in light of these simulations, we discuss how to best identify achromatic breaks in afterglow light curves via multi-wavelength analysis.