A1 Refereed original research article in a scientific journal
SN 2015BN: A Detailed Multi-wavelength View of a Nearby Superluminous Supernova
Authors: Nicholl M., Berger E., Smartt S. J., Margutti R., Kamble A., Alexander K. D., Chen T.-W., Inserra C., Arcavi I., Blanchard P. K., Cartier R., Chambers K. C., Childress M. J., Chornock R., Cowperthwaite P. S., Drout M., Flewelling H. A., Fraser M., Gal-Yam A., Galbany L., Harmanen J., Holoien T. W.-S., Hosseinzadeh G., Howell D. A., Huber M. E., Jerkstrand A., Kankare E., Kochanek C. S., Lin Z.-Y., Lunnan R., Magnier E. A., Maguire K., McCully C., McDonald M., Metzger B. D., Milisavljevic D., Mitra A., Reynolds T., Saario J., Shappee B. J., Smith K. W., Valenti S., Villar V. A., Waters C., Young D. R.
Publisher: IOP PUBLISHING LTD
Publication year: 2016
Journal: Astrophysical Journal
Article number: 39
Volume: 826
Issue: 1
Number of pages: 31
ISSN: 0004-637X
DOI: https://doi.org/10.3847/0004-637X/826/1/39
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.
