Nicholl, MatthewBerger, EdoSmartt, S. J.Margutti, R.Kamble, AtishAlexander, KateChen, T.-W.Inserra, C.Arcavi, I.Blanchard, PeterCartier, R.Chambers, K. C.Childress, M. J.Chornock, R.Cowperthwaite, PhilipDrout, 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.2017-03-032016Nicholl, M., E. Berger, S. J. Smartt, R. Margutti, A. Kamble, K. D. Alexander, T.-W. Chen, et al. 2016. “SN 2015bn: A Detailed Multi-wavelength View of a Nearby Superluminous Supernova.” The Astrophysical Journal 826 (1) (July 18): 39. doi:10.3847/0004-637x/826/1/39.1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:30510189We 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 (${M}_{U}\approx -23.1$) and in a fainter galaxy (${M}_{B}\approx -16.0$) than other SLSNe at $z\sim 0.1$. 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 $\gtrsim 10$ M ${}_{\odot }$ stripped progenitor exploding with $\sim {10}^{51}$ 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 ${}_{\odot }$ of dense, inhomogeneous circumstellar material—can be tested with continuing radio follow-up.en-USsupernovae: generalsupernovae: individual: SN 2015bnJournal Article2017-03-0310.3847/0004-637x/826/1/39