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The Two-Component Afterglow of Swift GRB 050802

S. R. OatesMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTM. de PasqualeMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTA. J. BlustinMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTSilvia ZaneMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTK. McGowanMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTK. O. MasonSchool of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJT. PooleMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTP. SchadyMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTP. W. A. RomingMullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NTA. FalconeDepartment of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USAN. GehrelsDepartment of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH

2012en

ABI

Annotatsiya

This paper investigates GRB 050802, one of the best examples of a Swift gammaray burst afterglow that shows a break in the X-ray lightcurve, while the optical counterpart decays as a single power-law. This burst has an optically bright afterglow of 16.5 magnitude, detected throughout the 170- 650nm spectral range of the UVOT on-board Swift. Observations began with the XRT and UVOT telescopes 286 s after the initial trigger and continued for 1.2 × 10 6 s. The X-ray lightcurve consists of three power-law segments: a rise until 420s, followed by a slow decay with α2 = 0.63 ± 0.03 until 5000s, after which, the lightcurve decays faster with a slope of α3 = 1.59 ± 0.03. The optical lightcurve decays as a single power-law with αO =0.82 ± 0.03 throughout the observation. The X-ray data on their own are consistent with the break at 5000s being due to the end of energy injection. Modelling the optical to X-ray spectral energy distribution, we find that the optical afterglow can not be produced by the same component as the X-ray emission at late times, ruling out a single component afterglow. We therefore considered two-component jet models and find that the X-ray

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