SwiftPanchromatic Observations of the Bright Gamma‐Ray Burst GRB 050525a

• DOI: 10.1086/498425
• Publication Date: 2006-01-25T15:23:56Z
• Authors: A. J. Blustin; D. Band; S. Barthelmy; P. Boyd; M. Capalbi; S. T. Holland; F. E. Marshall; K. O. Mason; M. Perri; T. Poole; P. Roming; S. Rosen; P. Schady; M. Still; B. Zhang; L. Angelini; L. Barbier; A. Beardmore; A. Breeveld; D. N. Burrows; J. R. Cummings; J. Canizzo; S. Campana; M. M. Chester; G. Chincarini; L. R. Cominsky; A. Cucchiara; M. de Pasquale; E. E. Fenimore; N. Gehrels; P. Giommi; M. Goad; C. Gronwall; D. Grupe; J. E. Hill; D. Hinshaw; S. Hunsberger; K. C. Hurley; M. Ivanushkina; J. A. Kennea; H. A. Krimm; P. Kumar; W. Landsman; V. La Parola; C. B. Markwardt; K. McGowan; P. Meszaros; T. Mineo; A. Moretti; A. Morgan; J. Nousek; P. T. O’Brien; J. P. Osborne; K. Page; M. J. Page; D. M. Palmer; A. M. Parsons; J. Rhoads; P. Romano; T. Sakamoto; G. Sato; G. Tagliaferri; J. Tueller; A. A. Wells; N. E. White
• Keywords: Science & Technology; Astrophysics (astro-ph); PEAK LUMINOSITY; GRB-990123; FOS: Physical sciences; X-rays : individual (GRB 050525a); GRB-021211; shock waves; Astronomy & Astrophysics; Astrophysics; AFTERGLOW LIGHT CURVES; 01 natural sciences; GRB 050525A; ENERGY; MODEL; Physical Sciences; galaxies : distances and redshifts; gamma rays : bursts; OPTICAL AFTERGLOWS; 0103 physical sciences; astrometry; SPECTRA; REVERSE-SHOCK

The bright gamma-ray burst GRB050525a has been detected with the Swift observatory, providing unique multiwavelength coverage from the very earliest phases of the burst. The X-ray and optical/UV afterglow decay light curves both exhibit a steeper slope ~0.15 days after the burst, indicative of a jet break. This jet break time combined with the total gamma-ray energy of the burst constrains the opening angle of the jet to be 3.2 degrees. We derive an empirical `time-lag' redshift from the BAT data of z_hat = 0.69 +/- 0.02, in good agreement with the spectroscopic redshift of 0.61. Prior to the jet break, the X-ray data can be modelled by a simple power law with index alpha = -1.2. However after 300 s the X-ray flux brightens by about 30% compared to the power-law fit. The optical/UV data have a more complex decay, with evidence of a rapidly falling reverse shock component that dominates in the first minute or so, giving way to a flatter forward shock component at later times. The multiwavelength X-ray/UV/Optical spectrum of the afterglow shows evidence for migration of the electron cooling frequency through the optical range within 25000 s. The measured temporal decay and spectral indices in the X-ray and optical/UV regimes compare favourably with the standard fireball model for Gamma-ray bursts assuming expansion into a constant density interstellar medium.<br/>31 pages, 7 figures, referee comments implemented, typo corrected in author list, accepted by ApJ<br/>