Super-luminous supernovae from PESSTO
  We present optical spectra and light curves for three hydrogen-poor
super-luminous supernovae followed by the Public ESO Spectroscopic Survey of
Transient Objects (PESSTO). Time series spectroscopy from a few days after
maximum light to 100 days later shows them to be fairly typical of this class,
with spectra dominated by Ca II, Mg II, Fe II and Si II, which evolve slowly
over most of the post-peak photospheric phase. We determine bolometric light
curves and apply simple fitting tools, based on the diffusion of energy input
by magnetar spin-down, 56Ni decay, and collision of the ejecta with an opaque
circumstellar shell. We investigate how the heterogeneous light curves of our
sample (combined with others from the literature) can help to constrain the
possible mechanisms behind these events. We have followed these events to
beyond 100-200 days after peak, to disentangle host galaxy light from fading
supernova flux and to differentiate between the models, which predict diverse
behaviour at this phase. Models powered by radioactivity require unrealistic
parameters to reproduce the observed light curves, as found by previous
studies. Both magnetar heating and circumstellar interaction still appear to be
viable candidates. A large diversity is emerging in observed tail-phase
luminosities, with magnetar models failing in some cases to predict the rapid
drop in flux. This would suggest either that magnetars are not responsible, or
that the X-ray flux from the magnetar wind is not fully trapped. The light
curve of one object shows a distinct re-brightening at around 100d after
maximum light. We argue that this could result either from multiple shells of
circumstellar material, or from a magnetar ionisation front breaking out of the
ejecta.
