PS1-14bj: A Hydrogen-poor Superluminous Supernova With a Long Rise and Slow Decay

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

Abstract

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 $\gtrsim 125$ rest-frame days, and exponential decline out to ~250 days past peak at a measured rate of $0.01\,\mathrm{mag}\,{\mathrm{day}}^{-1}$, 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 (${L}_{\mathrm{peak}}\simeq 4.6\times {10}^{43}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for $\gt 200$ 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.

Citation

Lunnan, R., Chornock, R., Berger, E., Milisavljevic, D., Jones, D., Rest, A., …Waters, C. (2016). PS1-14bj: A Hydrogen-poor Superluminous Supernova With a Long Rise and Slow Decay. Astrophysical Journal, 831(2), Article 144. https://doi.org/10.3847/0004-637x/831/2/144

• Journal Article Type: Article
• Acceptance Date: Aug 25, 2016
• Online Publication Date: Nov 3, 2016
• Publication Date: Nov 3, 2016
• Deposit Date: Nov 21, 2016
• Publicly Available Date: Nov 29, 2016
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 831
• Issue: 2
• Article Number: 144
• DOI: https://doi.org/10.3847/0004-637x/831/2/144
• Public URL: https://durham-repository.worktribe.com/output/1392893