Testing the Curvature Effect and Internal Origin of Gamma-Ray Burst Prompt Emissions and X-ray Flares with Swift Data

The X-ray light curves of many gamma-ray bursts (GRBs) observed by the Swift X-Ray Telescope (XRT) have a very steep-decay component (tail) following the prompt gamma-rays in the early phase and have some erratic flares occurring at a time from ∼ 10 up to ∼ 10 seconds. Based on the assumption that these prompt emission tails and flares are of “internal” origin and that their decline behaviors are dominated by the curvature effect of the fireball, we present a selfconsistency test for this scenario with a sample of 36 prompt-emission-tails/flares in 22 GRB XRT light curves. The curvature effect suggests that the temporal decay slope of the late steep-decay part of the light curves is α = 2 + β, where β is the X-ray spectral index. We derive the zero time (t0) for each steep decay component by fitting the light curves with the constraint of α = 2+β. Our results show that the t0’s of the prompt emission tails and the tails of well-separated flares are usually at the rising segment of the last pulse of the prompt emission or the corresponding X-ray flare, being self-consistent with the expectation of the internal dissipation models for the prompt emission and X-ray flares. Our results