Curvature Effect of a Non-Power-Law Spectrum and Spectral Evolution of GRB X-Ray Tails

TL;DR

This paper explores how a non-power-law spectrum with an exponential cutoff can explain the spectral evolution and lightcurve decay in GRB X-ray tails, challenging simpler power-law models.

Contribution

It introduces a curvature effect model based on a non-power-law spectrum with an exponential cutoff, tested against Swift/XRT GRB data.

Findings

The model reproduces observed lightcurves and spectral evolution of several GRBs.

GRB 050814 exemplifies the model's effectiveness.

Non-power-law spectra can better explain spectral evolution in GRB tails.

Abstract

The apparent spectral evolution observed in the steep decay phase of many GRB early afterglows raises a great concern of the high-latitude "curvature effect" interpretation of this phase. However, previous curvature effect models only invoked a simple power law spectrum upon the cessation of the prompt internal emission. We investigate a model that invokes the "curvature effect" of a more general non-power-law spectrum and test this model with the Swift/XRT data of some GRBs. We show that one can reproduce both the observed lightcurve and the apparent spectral evolution of several GRBs using a model invoking a power-law spectrum with an exponential cut off. GRB 050814 is presented as an example.