PS1-14bj: A hydrogen-poor superluminous supernova with a long rise and slow decay

R. Lunnan, R. Chornock, E. Berger, D. Milisavljevic, D. O. Jones, A. Rest, W. Fong, C. Fransson, R. Margutti, M. R. Drout, P. K. Blanchard, P. Challis, P. S. Cowperthwaite, R. J. Foley, R. P. Kirshner, N. Morrell, A. G. Riess, K. C. Roth, D. Scolnic, S. J. SmarttK. W. Smith, V. A. Villar, K. C. Chambers, P. W. Draper, M. E. Huber, N. Kaiser, R. P. Kudritzki, E. A. Magnier, N. Metcalfe, C. Waters

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We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift z = 0.5215 discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out because of its extremely slow evolution, with an observed rise of ≳125 rest-frame days, and exponential decline out to ∼250 days past peak at a measured rate of 0.01 mag day-1, consistent with fully trapped 56Co decay. This is the longest rise time measured in an SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) models. Compared to other slowly evolving SLSNe, it is spectroscopically similar to the prototype SN 2007bi at maximum light, although lower in luminosity (Lpeak≃4.6×1043 erg s-1) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for days past peak, and strong emission lines from [O iii] λ5007 and [O iii] λ4363 with a velocity width of ∼3400 km s-1 in its late-time spectra. These both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple 56Ni-powered/PISN interpretation. A modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [O iii] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. Alternatively, the late-time heating could be due to interaction with a shell of H-poor circumstellar material.

Original languageEnglish (US)
Article number144
JournalAstrophysical Journal
Issue number2
StatePublished - Nov 10 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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