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 M _ { u } = -21.4 mag and bolometric luminosity of 8 \times 10 ^ { 43 } ergs ^ { -1 } before settling onto a relatively shallow gradient of decline .
The observed decline is significantly slower than those of the superluminous type Ic SNe which have been the focus of much recent attention .
Spectroscopic similarities with the lower redshift SN2007bi and a decline rate similar to ^ { 56 } Co decay timescale 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 days before peak to 230 days 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 superluminous Ic supernovae , and the lightcurve 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 restframe UV data and allows us to compare it with the superluminous SNe recently found at high redshifts between z = 2 - 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 .