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tokens: We acknowledge Matthew Bayliss, Kathy Cooksey, Francesco Di Mille, Steven Elhert, Michael Florian, Tolga Guver, Traci Johnson, Dan Kelson, Michael McDonald, Andy Monson, David Osip, Benjamin Rackham, Nathan Sanders, Anil Seth, Meghin Spencer, Brian Stalder, Tony Stark, Rik Williams, and Amanda Zangari for their assistance in Magellan target-of-opportunity observations. Partial support for this work was provided by NASA through Einstein Postdoctoral Fellowship grant number PF4-150121 and Chandra Award Number G04-15055X, issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. B.A.Z. acknowledges support from NSF grant AST-1302954, E.B. acknowledges partial support from NSF grant AST-1107973, and R.M. acknowledges support from the James Arthur Fellowship at NYU. Additional support was provided by several NASA/ Swift grants. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. The scientific results reported in this article are in part based on observations made by the Chandra X-ray Observatory and data obtained from the Chandra Data Archive. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. Based on observations obtained at the Gemini Observatory acquired through the Gemini Science Archive and processed using the Gemini IRAF package which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), the Ministèrio da Ciência, Tecnologia e Inovação (Brazil), and the Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.