PS1-14bj: A Hydrogen-Poor Superluminous Supernova with a Long Rise and Slow Decay

Creators: Lunnan, R.

Abstract

We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift z = 0.5215 discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out because of its extremely slow evolution, with an observed rise of ≳ 125 rest-frame days, and exponential decline out to ~250 days past peak at a measured rate of 0.01 mag day^(-1), consistent with fully trapped ^(56)Co decay. This is the longest rise time measured in an SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) models. Compared to other slowly evolving SLSNe, it is spectroscopically similar to the prototype SN 2007bi at maximum light, although lower in luminosity (L_(peak) ≃ 4.6 x 10^(43) erg s(-1)) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for >200 days past peak, and strong emission lines from [O III] λ5007 and [O III] λ4363 with a velocity width of ~3400 km s^(−1) in its late-time spectra. These both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple ^(56)Ni-powered/PISN interpretation. A modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [O III] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. Alternatively, the late-time heating could be due to interaction with a shell of H-poor circumstellar material.

Additional Information

© 2016 The American Astronomical Society. Received 2016 May 17; revised 2016 August 23; accepted 2016 August 25; published 2016 November 3. We thank Dan Kasen and Alexandra Kozyreva for providing their theoretical PISN light curves, Andy Monson for help with processing the FourStar data, and Robert Quimby, Dan Perley, Matt Nicholl, Avishay Gal-Yam, and Lin Yan for helpful discussions. R.L. acknowledges helpful interactions with Dan Kasen, Lars Bildsten, and Eliot Quataert at a PTF Theory Network Retreat, which was funded by the Gordon and Betty Moore Foundation through Grant GBMF5076. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, and the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. Based in part on observations obtained under PIDs GN-2015A-FT-1 (PI: R.L.) and GN-2014A-Q-76/GS-2014A-Q-63 (PI: R.C.) 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), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. This work was supported in part by the Fermi National Accelerator Laboratory which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. This work is based in part on observations obtained at the MDM Observatory, operated by Dartmouth College, Columbia University, the Ohio State University, Ohio University, and the University of Michigan. This work was supported in part by the GROWTH project funded by the National Science Foundation under Grant No. 1545949. This work was supported in part by National Science Foundation Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics. The CfA Supernova Program is supported by NSF grants AST1211196 and AST156854 to the Harvard College Observatory. S.J.S. acknowledges funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement No. [291222] and STFC grants ST/I001123/1 and ST/L000709/1. Some of the computations in this paper were run on the Odyssey cluster supported by the FAS Division of Science, Research Computing Group at Harvard University. This research has made use of NASA's Astrophysics Data System. Facilities: PS1 - Panoramic Survey Telescope and Rapid Response System Telescope #1 (Pan-STARRS), MMT - MMT at Fred Lawrence Whipple Observatory, Magellan:Baade - Magellan I Walter Baade Telescope, Magellan:Clay - Magellan II Landon Clay Telescope, Gemini:Gillett - Gillett Gemini North Telescope, Gemini:South - Gemini South Telescope, LBT - Large Binocular Telescope Observatory, McGraw-Hill - MDM Observatory's 1m McGraw-Hill Telescope, Hiltner - MDM Observatory's 2.4m Hiltner Telescope.

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