High-latitude emission of a non-power-law spectrum and spectral evolution of GRB X-ray tails

Abstract

The apparent spectral evolution observed in the steep decay phase of many GRB earlyX-ray 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 the "curvature effect" model of a more general non-power-law spectrum and and test this model with the Swift/XRT observations By comparing the simulated lightcurves/spectra with the observed ones, we show that one can reproduce both the observed lightcurve and the apparent spectral evolution of GRB 050814 using a model invoking a cut-off power-law spectrum. This suggests that at least for some GRBs, the fast spectral evolution in the steep-decay phase can be explained by the curvature effect of a non-power-law spectrum. © 2009 American Institute of Physics.