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|Title:||Spectral evolution and the onset of the X-ray GRB afterglow|
|Authors:||Evans, P. A.|
Osborne, J. P.
O'Brien, P. T.
|Publisher:||American Institute of Physics (AIP)|
|Citation:||AIP Conference Proceedings, Volume 1358, Issue 1., GAMMA RAY BURSTS 2010, (2011), 117|
|Abstract:||Based on light curves from the Swift Burst Analyser, we investigate whether a ‘dip’ feature commonly seen in the early‐time hardness ratios of Swift‐XRT data could arise from the juxtaposition of the decaying prompt emission and rising afterglow. We are able to model the dip as such a feature, assuming the afterglow rises as predicted by Sari and Piran . Using this model we measure the initial bulk Lorentz factor of the fireball. For a sample of 23 GRBs we find a median value of Γ[subscript: 0] = 225, assuming a constant‐density circumburst medium; or Γ[subscript: 0] = 93 if we assume a wind‐like medium.|
|Rights:||Creative Commons “Attribution Non-Commercial No Derivatives” licence CC BY-NC-ND, further details of which can be found via the following link: http://creativecommons.org/licenses/by-nc-nd/4.0/ Archived with reference to SHERPA/RoMEO and publisher website.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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