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SUPERLUMINOUS SUPERNOVA SN 2015bn in the NEBULAR PHASE: EVIDENCE for the ENGINE-POWERED EXPLOSION of A STRIPPED MASSIVE STAR

Nicholl, M and Berger, E and Margutti, R and Chornock, R and Blanchard, PK and Jerkstrand, A and Smartt, SJ and Arcavi, I and Challis, P and Chambers, KC and Chen, TW and Cowperthwaite, PS and Gal-Yam, A and Hosseinzadeh, G and Howell, DA and Inserra, C and Kankare, E and Magnier, EA and Maguire, K and Mazzali, PA and McCully, C and Milisavljevic, D and Smith, KW and Taubenberger, S and Valenti, S and Wainscoat, RJ and Yaron, O and Young, DR (2016) SUPERLUMINOUS SUPERNOVA SN 2015bn in the NEBULAR PHASE: EVIDENCE for the ENGINE-POWERED EXPLOSION of A STRIPPED MASSIVE STAR. ASTROPHYSICAL JOURNAL LETTERS, 828 (2). ISSN 2041-8205

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Abstract

© 2016. The American Astronomical Society. All rights reserved.We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova (SLSN) SN 2015bn, at redshift z = 0.1136, spanning +250-400 days after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag (100 days)-1 to 1.7 mag (100 days)-1, suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium, and magnesium. There are no obvious signatures of circumstellar interaction or large 56Ni mass. We show that the spectrum at +400 days is virtually identical to a number of energetic SNe Ic such as SN 1997dq, SN 2012au, and SN 1998bw, indicating similar core conditions and strengthening the link between "hypernovae"/long gamma-ray bursts and SLSNe. A single explosion mechanism may unify these events that span absolute magnitudes of -22 < M B < -17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7-30 M o of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O i λ7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: IOP PUBLISHING LTD
Date Deposited: 13 Apr 2017 12:37
Last Modified: 13 Apr 2017 12:37
DOI or Identification number: 10.3847/2041-8205/828/2/L18
URI: http://researchonline.ljmu.ac.uk/id/eprint/6258

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