SN 2015bn: a detailed multi-wavelength view of a nearby superluminous supernova

M. Nicholl, E. Berger, S. J. Smartt, R. Margutti, A. Kamble, K. D. Alexander, T. -W. Chen, C. Inserra, I. Arcavi, P. K. Blanchard, R. Cartier, K. C. Chambers, M. J. Childress, R. Chornock, P. S. Cowperthwaite, M. Drout, H. A. Flewelling, M. Fraser, A. Gal-Yam, L. GalbanyJ. Harmanen, T. W. -S. Holoien, G. Hosseinzadeh, D. A. Howell, M. E. Huber, A. Jerkstrand, E. Kankare, C. S. Kochanek, Z. -Y. Lin, R. Lunnan, E. A. Magnier, K. Maguire, C. McCully, M. McDonald, B. D. Metzger, D. Milisavljevic, A. Mitra, T. Reynolds, J. Saario, B. J. Shappee, K. W. Smith, S. Valenti, V. A. Villar, C. Waters, D. R. Young

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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 (MU ≈ -23.1) and in a fainter galaxy (MB ≈ -16.0) than other SLSNe at z ∼ 0.1. We used this opportunity to collect the most extensive dataset 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 ∼1051 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.
Original languageEnglish
Article number39
Number of pages31
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 18 Jul 2016


  • astro-ph.SR
  • astro-ph.CO
  • astro-ph.HE
  • supernovae: general
  • supernovae: individual (SN 2015bn)


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