Slowly fading super-luminous supernovae that are not pair-instability explosions.
Nature 502:7471 (2013) 346-349
Authors:
M Nicholl, SJ Smartt, A Jerkstrand, C Inserra, M McCrum, R Kotak, M Fraser, D Wright, T-W Chen, K Smith, DR Young, SA Sim, S Valenti, DA Howell, F Bresolin, RP Kudritzki, JL Tonry, ME 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, G Narayan, CW Stubbs, RJ Foley, R Lunnan, A Soderberg, N Sanders, D Milisavljevic, R Margutti, RP Kirshner, N Elias-Rosa, A Morales-Garoffolo, S Taubenberger, MT Botticella, S Gezari, Y Urata, S Rodney, AG Riess, D Scolnic, WM Wood-Vasey, WS Burgett, K Chambers, HA Flewelling, EA Magnier, N Kaiser, N Metcalfe, J Morgan, PA Price, W Sweeney, C Waters
Abstract:
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 65-130 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 (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, 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 6 × 10(-6) times that of the core-collapse rate.
