McCrum, M., Smartt, S. J., Kotak, R., Rest, A., Jerkstrand, A., Inserra, C., Rodney, S. A., Chen, T. -W, Howell, D. A., Huber, M. E., Pastorello, A., Tonry, J. L., Bresolin, F., Kudritzki, R. -P, Chornock, R., Berger, E., Smith, K., Botticella, M. T., Foley, R. J., Fraser, M., Milisavljevic, D., Nicholl, M., Riess, A. G., Stubbs, C. W., Valenti, S. et al. 2014. "The superluminous supernova PS1-11ap: bridging the gap between low and high redshift." Monthly Notices of the Royal Astronomical Society 437:656-674. https://doi.org/10.1093/mnras/stt1923
We present optical photometric and spectroscopic coverage of the superluminous supernova (SLSN) PS1-11ap, discovered with the Pan-STARRS1 Medium Deep Survey at z = 0.524. This intrinsically blue transient rose slowly to reach a peak magnitude of Mu = -21.4 mag and bolometric luminosity of 8 × 1043 erg s-1 before settling on to a relatively shallow gradient of decline. The observed decline is significantly slower than those of the SLSNe-Ic which have been the focus of much recent attention. Spectroscopic similarities with the lower redshift SN2007bi and a decline rate similar to 56Co decay time-scale initially indicated that this transient could be a candidate for a pair instability supernova (PISN) explosion. Overall the transient appears quite similar to SN2007bi and the lower redshift object PTF12dam. The extensive data set, from 30 d before peak to 230 d after, allows a detailed and quantitative comparison with published models of PISN explosions. We find that the PS1-11ap data do not match these model explosion parameters well, supporting the recent claim that these SNe are not pair instability explosions. We show that PS1-11ap has many features in common with the faster declining SLSNe-Ic, and the light-curve evolution can also be quantitatively explained by the magnetar spin-down model. At a redshift of z = 0.524, the observer-frame optical coverage provides comprehensive rest-frame UV data and allows us to compare it with the SLSNe recently found at high redshifts between z = 2 and 4. While these high-z explosions are still plausible PISN candidates, they match the photometric evolution of PS1-11ap and hence could be counterparts to this lower redshift transient.
