AAS 207th Meeting, 8-12 January 2006
Session 158 GRB: Short Bursts and Panchromatic Observations
Oral, Wednesday, 2:00-3:30pm, January 11, 2006, Virginia

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[158.06] Swift\/ Panchromatic Observations of the Bright Gamma-Ray Burst GRB 050525A

S. T. Holland (NASA's GSFC & USRA), Swift Science Team

The bright gamma-ray burst GRB 050525A was observed with the Swift\/ observatory, providing unique multiwavelength coverage from the very earliest phases of the burst. The X\/-ray and optical/ultraviolet afterglow decay light curves exhibit an achromatic break approximately 0.15 days after the burst. The timing of this break, combined with the total gamma-ray energy of the burst, constrains the opening angle of the jet to be 2.5 degrees. Prior to the jet break the X\/-ray data can be modelled by a power law with an index of \alpha = -1.2. There is a short X\/-ray flare at 300 s after the burst. The optical/ultraviolet data have a complex decay, with evidence of a rapidly falling reverse shock component that dominates in the first minute and a flatter forward shock at later times. The multiwavelength X\/-ray/ultraviolet/optical spectrum of the afterglow shows evidence for a cooling break moving through the optical between 800 and 25\,000 s after the burst. The measured temporal decay and spectral indices in the X\/-ray and optical/ultraviolet regimes agree with the standard fireball model for gamma-ray bursts, assuming expansion into a constant density interstellar medium.

The Swift\/ programme is supported by NASA, PPARC, and ASI (contract number I/R/039/04).

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