Xue-Feng Wu, Shu-Jin Hou, Wei-Hua Lei
The most interesting discovery in GRB 121027A is the giant X-ray bump detected by Swift/XRT. The X-ray afterglow re-brightens sharply at ~ 1000 s since the trigger by more than two orders of magnitude in less than 200 s. This X-ray bump lasts for more than 10 ks. It is quite different with typical X-ray flares. In this paper we propose a fallback accretion model to interpret this X-ray bump within the context of collapse of a massive star for long duration gamma-ray bursts. The required fallback radius ~ 3.5e10 cm and mass ~ 2.6 solar mass imply that a significant part of the helium envelope should be survived through the mass loss during the last stage of the massive progenitor of GRB 121027A.
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http://arxiv.org/abs/1302.4878
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