C. Inserra, S. J. Smartt, A. Jerkstrand, S. Valenti, M. Fraser, D. Wright, K. Smith, T. -W. Chen, R. Kotak, A. Pastorello, M. Nicholl, F. Bresolin, R. P. Kudritzki, S. Benetti, M. T. Botticella, W. S. Burgett, K. C. Chambers, M. Ergon, H. Flewelling, J. P. U. Fynbo, S. Geier, K. W. Hodapp, A. Howell, M. Huber, N. Keiser, G. Leloudas, L. Magill, E. A. Magnier, M. G. McCrumm, N. Metcalfe, P. A. Price, A. Rest, J. Sollerman, W. Sweeney, F. Taddia, S. Taubenberger, J. L. Tonry, R. J. Wainscoat, C. Waters, D. Young
We report extensive observational data for five of the lowest redshift Super-Luminous Type Ic Supernovae (SL-SNe Ic) discovered to date. The five SNe, namely SN 2010md, SN 2011ke, SN 2011kg, SN 2011kf and SN 2012il show absolute peak magnitudes of $-21.73\lesssim M_{g}$(mag) $\lesssim -20.42$ and spectroscopic evolution similar to that of SN 2010gx. Photometric imaging of the transients at 50 to 230 days after peak combined with host galaxy subtraction reveals a luminous tail phase for four of these SL-SNe. A high resolution, optical and near infrared spectrum from xshooter provides detection of a broad He I $\lambda$10830 emission line in the spectrum of SN 2012il at +50d after peak, revealing that at least some SL-SNe Ic are not completely helium free. At first sight, the tail luminosity decline rates that we measure are consistent with the radioactive decay of 56Co, and would require 1-4 \M of 56Ni to produce the luminosity. These quite large 56Ni masses cannot be made consistent with the short diffusion times at peak, and indeed are insufficient to power the peak luminosity. We instead favour energy deposition by newborn magnetars as the power source for these objects. A semi-analytical diffusion model with energy input from the spin-down of a magnetar reproduces the extensive lightcurve data well. The model predictions of ejecta velocities and temperatures which are required are in reasonable agreement with those determined from our photometric and spectroscopic observations. We derive magnetar energies of $0.4\lesssim E$($10^{51}$erg) $\lesssim17$ and ejecta masses of $2.3\lesssim M_{ej}$(\M) $\lesssim 9.7$. The sample of five SL-SNe Ic presented here, combined with SN 2010gx - the best sampled SL-SNe Ic so far - point toward an explosion driven by a magnetar as a viable explanation for all SL-SNe Ic.
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http://arxiv.org/abs/1304.3320
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