SN 2015BN: A Detailed Multi-wavelength View of a Nearby Superluminous Supernova
Abstract
We present observations of SN 2015bn (=PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift z = 0.1136. As well as being one of the closest SLSNe I yet discovered, it is intrinsically brighter ({M}U≈ -23.1) and in a fainter galaxy ({M}B≈ -16.0) than other SLSNe at z∼ 0.1. We used this opportunity to collect the most extensive data set for any SLSN I to date, including densely sampled spectroscopy and photometry, from the UV to the NIR, spanning -50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30-50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20-30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a ≳ 10 M {}⊙ stripped progenitor exploding with ∼ {10}51 erg kinetic energy, forming a magnetar with a spin-down timescale of ∼20 days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario—interaction with ∼20 M {}⊙ of dense, inhomogeneous circumstellar material—can be tested with continuing radio follow-up.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2016
- DOI:
- 10.3847/0004-637X/826/1/39
- arXiv:
- arXiv:1603.04748
- Bibcode:
- 2016ApJ...826...39N
- Keywords:
-
- supernovae: general;
- supernovae: individual: SN 2015bn;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Slightly updated to match published version