Superluminous Supernova SN 2015bn in the Nebular Phase: Evidence for the Engine-powered Explosion of a Stripped Massive Star

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Authors

  • E. Berger
  • R. Margutti
  • R. Chornock
  • P. K. Blanchard
  • A. Jerkstrand
  • S. J. Smartt
  • I. Arcavi
  • P. Challis
  • K. C. Chambers
  • T. -W. Chen
  • P. S. Cowperthwaite
  • A. Gal-Yam
  • G. Hosseinzadeh
  • D. A. Howell
  • C. Inserra
  • E. Kankare
  • E. A. Magnier
  • K. Maguire
  • P. A. Mazzali
  • C. McCully
  • D. Milisavljevic
  • K. W. Smith
  • S. Taubenberger
  • S. Valenti
  • R. J. Wainscoat
  • O. Yaron
  • D. R. Young

Colleges, School and Institutes

Abstract

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 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....

Details

Original languageUndefined/Unknown
JournalAstrophysical Journal Letters
Publication statusPublished - Sep 2016