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Published March 1, 2018 | Published
Journal Article Open

Spectra of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory

Abstract

Most Type I superluminous supernovae (SLSNe-I) reported to date have been identified by their high peak luminosities and spectra lacking obvious signs of hydrogen. We demonstrate that these events can be distinguished from normal-luminosity SNe (including Type Ic events) solely from their spectra over a wide range of light-curve phases. We use this distinction to select 19 SLSNe-I and four possible SLSNe-I from the Palomar Transient Factory archive (including seven previously published objects). We present 127 new spectra of these objects and combine these with 39 previously published spectra, and we use these to discuss the average spectral properties of SLSNe-I at different spectral phases. We find that Mn ii most probably contributes to the ultraviolet spectral features after maximum light, and we give a detailed study of the O ii features that often characterize the early-time optical spectra of SLSNe-I. We discuss the velocity distribution of O ii, finding that for some SLSNe-I this can be confined to a narrow range compared to relatively large systematic velocity shifts. Mg ii and Fe ii favor higher velocities than O ii and C ii, and we briefly discuss how this may constrain power-source models. We tentatively group objects by how well they match either SN 2011ke or PTF12dam and discuss the possibility that physically distinct events may have been previously grouped together under the SLSN-I label.

Additional Information

© 2018 American Astronomical Society. Received 2017 September 13. Accepted 2018 January 25. Published 2018 February 27. The data presented herein were obtained in part at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We thank the following for assistance with some of the Lick and Keck observations and reductions: Kelsey Clubb, Ryan Foley, Christopher Griffith, Pat Kelly, Michael Kandrashoff, and Isaac Shivvers. The William Herschel Telescope is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Research at Lick Observatory is supported in part by a generous gift from Google. Support for HST programs GO-12223 and GO-12524 was provided by NASA through a grant from STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. M.S. acknowledges support from EU/FP7-ERC grant no [615929]. A.D.C. acknowledges support by the Weizmann Institute of Science Koshland Center for Basic Research. A.V.F.'s supernova research group at U.C. Berkeley is grateful for generous financial assistance from the Christopher R. Redlich Fund, the TABASGO Foundation, NSF grant AST-1211916, and the Miller Institute for Basic Research in Science (U.C. Berkeley). M.M.K. acknowledges support by the GROWTH project funded by NSF grant AST-1545949. J.C. acknowledges support from the Australian Research Council Future Fellowship, grant FT130101219. A.G.-Y. is supported by the EU via ERC grant No. 725161, the Quantum Universe I-Core program, the ISF, the BSF Transformative program and by a Kimmel award. We thank Melissa Graham for providing spectra of PTF12dam, PTF12gty, and PTF12hni.

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August 19, 2023
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October 18, 2023