Lag-luminosity relation in Gamma-Ray Burst X-ray flares

In strict analogy to prompt pulses, X‐ray flares observed by Swift‐XRT in long Gamma‐Ray Bursts define a lag‐luminosity relation: Lp,iso0.3−10 keV ∞tlag−0.95±0.23. The lag‐luminosity is proven to be a fundamental law extending ∼5 decades in time and ∼5 in energy. This is direct evidence that GRB X‐ray flares and prompt gamma‐ray pulses are produced by the same mechanism.