GRB 140515A at z = 6.33: Constraints on the end of reionization from a gamma-ray burst in a low hydrogen column density environment. arXiv: 1405.7400Chornock R., Berger E., Fox D. B., Fong W., Laskar T., Roth K. C., 2014, preprint (arxiv:1405.7400)Chornock R., Berger E.,...