A NEW POPULATION OF ULTRA-LONG DURATION GAMMA-RAY BURSTS

We thank D. A. Kann and the GROND team for sharing their photometric calibration and Jamie Kennea for providing information on the Swift slew strategy. A.J.L. acknowledges support from the Science and Technology Facilities Council (STFC, under grant ID ST/I001719/1) and is grateful to the Leverhulme Trust for a Philip Leverhulme Prize award. N.R.T., K.W., and P.T.O. thank STFC for support (grant ID ST/H001972/ 1). R.L.C.S. is supported by a Royal Society Dorothy Hodgkin Fellowship. The Dark Cosmology Centre is supported by the DNRF. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 288.D-5027. Support for programs 11734, 12438, and 12786 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5- 26555. Support for D.P. is provided by NASA through Hubble Fellowship grant HST-HF-51296.01-A awarded by the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., for NASA, under contract NAS 5-26555. Based on observations obtained at the Gemini Observatory, 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), Ministerio da Ci ´ encia, Tecnologia e Inova¸ ˆ cao˜ (Brazil), and Ministerio de Ciencia, Tecnolog´ıa e Innovacion´ Productiva (Argentina). These observations were obtained as part of programme IDs GN-2010B-Q-7, GN-2011A-Q-4, GS- 2011B-Q-7, GN-2011B-Q-34, and GS-2012A-Q-25. This work was made possible by contributions from Iniciativa Cientifica Milenio grant P10-064-F (Millennium Center for Supernova Science), wit