Lunnan, R.Chornock, R.Berger, EdoMilisavljevic, DannyJones, D. O.Rest, A.Fong, W.Fransson, C.Margutti, R.Drout, M. R.Blanchard, PeterChallis, P.Cowperthwaite, PhilipFoley, R. J.Kirshner, RobertMorrell, N.Riess, A. G.Roth, K. C.Scolnic, D.Smartt, S. J.Smith, K. W.Villar, AshleyChambers, K. C.Draper, P. W.Huber, M. E.Kaiser, N.Kudritzki, R.-P.Magnier, E. A.Metcalfe, N.Waters, C.2017-03-032016Lunnan, R., R. Chornock, E. Berger, D. Milisavljevic, D. O. Jones, A. Rest, W. Fong, et al. 2016. “PS1-14bj: A Hydrogen-poor Superluminous Supernova with a Long Rise and Slow Decay.” The Astrophysical Journal 831 (2) (November 3): 144. doi:10.3847/0004-637x/831/2/144.1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:30510190We 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 by its extremely slow evolution, with an observed rise of ∼ > 125 restframe 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 a 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, though lower in luminosity (Lpeak ≃ 4.6×1043ergs−1) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for > 200 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.en-USsupernovae: generalsupernovae: individual (PS1-14bj, LSQ14an)Journal Article2017-03-0310.3847/0004-637x/831/2/144