Observations of X-ray Flares from Gamma Ray Bursts

TL;DR

Swift-XRT observations reveal that a significant fraction of gamma-ray bursts exhibit X-ray flares with diverse timing and energetic properties, suggesting they originate from the same internal engine processes as the prompt emission.

Contribution

This study provides new observational evidence of X-ray flares in GRBs, highlighting their timing, energetics, and spectral features, and supports models linking flares to internal engine activity.

Findings

1/3-1/2 of GRBs show detectable X-ray flares

Flares can be as energetic as prompt emission

Flares occur up to 10^5 seconds after initial burst

Abstract

Swift-XRT observations of the X-ray emission from gamma ray bursts (GRBs) and during the GRB afterglow have led to many new results during the past two years. One of these exciting results is that approximately 1/3-1/2 of GRBs contain detectable X-ray flares. The mean fluence of the X-ray flares is ~10 times less than that of the initial prompt emission, but in some cases the flare is as energetic as the prompt emission itself. The flares display fast rises and decays, and they sometimes occur at very late times relative to the prompt emission (sometimes as late as 10^5 s after T_0) with very high peak fluxes relative to the underlying afterglow decay that has clearly begun prior to some flares. The temporal and spectral properties of the flares are found to favor models in which flares arise due to the same GRB internal engine processes that spawned the prompt GRB emission. Therefore, both long and short GRB internal engine models must be capable of producing high fluences in the X-ray band at very late times.