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Slowly fading super-luminous supernovae that are not pair-instability explosions

2013; Nature Portfolio; Volume: 502; Issue: 7471 Linguagem: Inglês

10.1038/nature12569

1476-4687

M. Nicholl, S. J. Smartt, A. Jerkstrand, C. Inserra, M. McCrum, R. Kotak, M. Fraser, D. E. Wright, T. W. Chen, K. Smith, D. R. Young, Stuart Sim, S. Valenti, D. A. Howell, Fabio Bresolin, Rolf‐Peter Kudritzki, J. Tonry, M. E. Huber, A. Rest, A. Pastorello, L. Tomasella, E. Cappellaro, S. Benetti, S. Mattila, E. Kankare, T. Kangas, G. Leloudas, J. Sollerman, F. Taddia, E. Berger, R. Chornock, Gautham Narayan, C. W. Stubbs, R. J. Foley, R. Lunnan, A. Soderberg, Nathan Sanders, D. Milisavljević, R. Margutti, R. P. Kirshner, N. Elias‐Rosa, A. Morales-Garoffolo, S. Taubenberger, M. T. Botticella, Suvi Gezari, Y. Urata, S. Rodney, Adam G. Riess, D. Scolnic, W. M. Wood‐Vasey, W. S. Burgett, K. C. Chambers, H. Flewelling, E. A. Magnier, N. Kaiser, N. Metcalfe, James P. Morgan, P. A. Price, William E. Sweeney, C. Waters,

Stellar, planetary, and galactic studies

Super-luminous supernovae that radiate more than 10^44 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-30 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to 56Fe via 56Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6x10^-6 times that of the core-collapse rate.