iPTF 16asu: A Luminous, Rapidly Evolving, and High-velocity Supernova

Creators: Whitesides, L.; Lunnan, R.; Kasliwal, M. M.; Blagorodnova, N.; Cao, Y.; Cook, D. O.; Kulkarni, S. R.; Masci, F.

Abstract

Wide-field surveys are discovering a growing number of rare transients whose physical origin is not yet well understood. Here we present optical and UV data and analysis of intermediate Palomar Transient Factory (iPTF) 16asu, a luminous, rapidly evolving, high-velocity, stripped-envelope supernova (SN). With a rest-frame rise time of just four days and a peak absolute magnitude of M_g = -20.4 mag, the light curve of iPTF 16asu is faster and more luminous than that of previous rapid transients. The spectra of iPTF 16asu show a featureless blue continuum near peak that develops into an SN Ic-BL spectrum on the decline. We show that while the late-time light curve could plausibly be powered by ^(56)Ni decay, the early emission requires a different energy source. Nondetections in the X-ray and radio strongly constrain the energy coupled to relativistic ejecta to be at most comparable to the class of low-luminosity gamma-ray bursts (GRBs). We suggest that the early emission may have been powered by either a rapidly spinning-down magnetar or by shock breakout in an extended envelope of a very energetic explosion. In either scenario a central engine is required, making iPTF 16asu an intriguing transition object between superluminous SNe, SNe Ic-BL, and low-luminosity GRBs.

Additional Information

© 2017 The American Astronomical Society. Received 2017 June 14; revised 2017 October 10; accepted 2017 November 6; published 2017 December 18. We thank the anonymous referee for constructive comments that improved the manuscript. We thank Iair Arcavi, Maria Drout, Avishay Gal-Yam, Raffaella Margutti, and Maryam Modjaz for helpful discussions and comments. R. L. acknowledges helpful discussions at the Munich Institute for Astro- and Particle Physics (MIAPP) workshop "Superluminous Supernovae in the Next Decade," supported by the MIAPP, of the DFG cluster of excellence "Origin and Structure of the Universe." We thank Harish Vedantham, Vikram Ravi, and Anna Ho for assisting with the observations presented in this paper. The Intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology; Los Alamos National Laboratory; the University of Wisconsin, Milwaukee; the Oskar Klein Center; the Weizmann Institute of Science; the TANGO Program of the University System of Taiwan; and the Kavli Institute for the Physics and Mathematics of the Universe. This work was supported by the GROWTH project, funded by the National Science Foundation under Grant No. 1545949. This work is partially based on data acquired with the Swift GO program 1215281 (Grant No. NNX16AN84G, PI: R. Lunnan). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. A. C. acknowledges support from the National Science Foundation CAREER Award No. 1455090. D. S. and D. F. gratefully acknowledge support from RSF Grant No. 17-12-01378. This work made use of the data products generated by the New York University SN group and released under DOI:10.5281/zenodo.58767, available at https://github.com/nyusngroup/SESNspectraLib based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: PO: 1.2 m - , PO: 1.5 m - , PO: Hale - , Keck: I - KECK I Telescope, Keck: II - KECK II Telescope, NOT - Nordic Optical Telescope, TNG - Telescopio Nazionale Galileo, Swift - Swift Gamma-Ray Burst Mission, VLA.

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