tokens: This research has made use of the following data and software packages: observations made by the Chandra X-ray Observatory, data obtained from the Chandra Data Archive, software provided by the Chandra X-ray Center (CXC) in the application package ciao , and software provided by the High Energy Astrophysics Science Archive Research Center in the heasoft package. We acknowledge extensive use of the ADS and arXiv. AB thanks G.R. Sivakoff and T.J. Maccarone for helpful discussions. COH acknowledges financial support from NSERC Discovery Grants, an Alberta Ingenuity New Faculty Award, and an Alexander von Humboldt Fellowship. ND acknowledges support via an EU Marie Curie Intra-European fellowship under contract no. FP-PEOPLE-2013-IEF-627148. LC acknowledges support from a Chandra grant associated with Obs.ID 15761. WCGH acknowledges support from STFC in the UK. This work was partially supported by the NSF through grant AST-1308124.
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