SUPERLUMINOUS SUPERNOVA SN 2015bn IN THE NEBULAR PHASE: EVIDENCE FOR THE ENGINE-POWERED EXPLOSION OF A STRIPPED MASSIVE STAR

Journal Article · Sat Sep 10 00:00:00 EDT 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8205/828/2/L18· OSTI ID:22654226

Nicholl, M.; Berger, E.; Blanchard, P. K.; Challis, P.; Cowperthwaite, P. S. ^[1]; Margutti, R. ^[2]; Chornock, R. ^[3]; Jerkstrand, A.; Smartt, S. J.; Inserra, C.; Kankare, E.; Maguire, K. ^[4]; Arcavi, I.; Hosseinzadeh, G.; Howell, D. A. ^[5]; Chambers, K. C.; Magnier, E. A. ^[6]; Chen, T. -W. ^[7]; Gal-Yam, A. ^[8]; others, and

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2. Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003 (United States)
3. Astrophysical Institute, Department of Physics and Astronomy, 251B Clippinger Lab, Ohio University, Athens, OH 45701 (United States)
4. Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN (United Kingdom)
5. Las Cumbres Observatory Global Telescope, 6740 Cortona Drive, Suite 102, Goleta, CA 93111 (United States)
6. Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)
7. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, D-85748, Garching (Germany)
8. Benoziyo Center for Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel)

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){sup −1} to 1.7 mag (100 days){sup −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 {sup 56}Ni 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 {sub B} < −17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7–30 M {sub ⊙} of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O i λ 7774 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.

• OSTI ID: 22654226
• Journal Information: Astrophysical Journal Letters, Vol. 828, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
CALCIUM
COSMIC GAMMA BURSTS
EMISSION
EXPLOSIONS
GAMMA RADIATION
HYDROGEN
INTERACTIONS
LUMINOSITY
MAGNESIUM
MASS
NICKEL 56
OPACITY
OXYGEN
RED SHIFT
SPECTRA
SPECTROSCOPY
SUPERNOVAE
VISIBLE RADIATION