Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 400, Issue 4, Pages 1829-1834Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2009.15555.x
Keywords
radiation mechanisms: non-thermal; ISM: jets and outflows; gamma-rays: bursts
Categories
Funding
- National Science Foundation [10673034, 10621303]
- National Basic Research Programme of China [2007CB815404, 2009CB824800]
- Danish National Research Foundation
- Chinese Academy of Sciences
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We present the prompt Burst Alert Telescope and afterglow X-ray Telescope data of Swift-discovered GRB 081109A up to similar to 5 x 105 s after the trigger, and the early ground-based optical followups. The temporal and spectral indices of the X-ray afterglow emission change remarkably. We interpret this as the gamma-ray burst jet first traversing the freely expanding supersonic stellar wind of the progenitor with density varying as proportional to r-2. Then, after approximately 300 s the jet traverses into a region of apparent constant density similar to that expected in the stalled-wind region of a stellar wind bubble or the interstellar medium. The optical afterglow data are generally consistent with such a scenario. Our best numerical model has a wind density parameter A(*) similar to 0.02, a density of the stalled wind n similar to 0.12 cm-3 and a transition radius similar to 4.5 x 1017 cm. Such a transition radius is smaller than that predicted by numerical simulations of the stellar wind bubbles and may be due to a rapidly evolving wind of the progenitor close to the time of its core-collapse.
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