Self-organized criticality in X-ray flares of gamma-ray-burst afterglows

• Published in: Nature physics Vol. 9; no. 8; pp. 465 - 467
• Main Authors: Wang, F. Y., Dai, Z. G.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2013; Nature Publishing Group
• Subjects: 639/33/34/864; 639/766/530/2803; Accretion disks; Afterglows; Astrophysics; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Emission; Emissions; Engines; Explosions; Flares; Frequency distribution; Gamma rays; High energy physics; letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Solar flares; Theoretical; X-rays
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2670

Gamma-ray bursts are the most energetic sources of radiation in the Universe, and half are followed by afterglows that include X-ray flares of mysterious origin. A statistical study of such X-ray flares reveals the same power-law behaviour as solar flares, which suggests a common underlying magnetic reconnection process. X-ray flares detected in nearly half of gamma-ray-burst (GRB) afterglows are one of the most intriguing phenomena in high-energy astrophysics 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . All of the observations indicate that the central engines of bursts, after the gamma-ray emission has ended, still have long periods of activity, during which energetic explosions eject relativistic materials, leading to late-time X-ray emission 2 , 9 , 10 . It is thus expected that X-ray flares provide important clues as to the nature of the central engines of GRBs, and more importantly, unveil the physical mechanism of the flares themselves, which has so far remained mysterious. Here we report statistical results of X-ray flares of GRBs with known redshifts, and show that X-ray flares and solar flares share three statistical properties: power-law frequency distributions for energies, durations and waiting times. All of the distributions can be well understood within the physical framework of a self-organized criticality (SOC) system. The statistical properties of X-ray flares of GRBs are similar to solar flares, and thus both can be attributed to a SOC process. Both types of flares may be driven by a magnetic reconnection process, but X-ray flares of GRBs are produced in ultra-strongly magnetized millisecond pulsars 11 , 12 or long-term hyperaccreting disks around stellar-mass black holes 13 .