  We study SN 2006oz, a newly-recognized member of the class of H-poor,
super-luminous supernovae. We present multi-color light curves from the SDSS-II
SN Survey, that cover the rise time, as well as an optical spectrum that shows
that the explosion occurred at z~0.376. We fitted black body functions to
estimate the temperature and radius evolution of the photosphere and used the
parametrized code SYNOW to model the spectrum. We constructed a bolometric
light curve and compared it with explosion models. The very early light curves
show a dip in the g- and r-bands and a possible initial cooling phase in the
u-band before rising to maximum light. The bolometric light curve shows a
precursor plateau with a duration of 6-10 days in the rest-frame. A lower limit
of M_u < -21.5 can be placed on the absolute peak luminosity of the SN, while
the rise time is constrained to be at least 29 days. During our observations,
the emitting sphere doubled its radius to 2x10^15 cm, while the temperature
remained hot at 15000 K. As for other similar SNe, the spectrum is best modeled
with elements including O II and Mg II, while we tentatively suggest that Fe
III might be present. We suggest that the precursor plateau might be related to
a recombination wave in a circumstellar medium (CSM) and discuss whether this
is a common property of all similar explosions. The subsequent rise can be
equally well described by input from a magnetar or by ejecta-CSM interaction,
but the models are not well constrained owing to the lack of post-maximum
observations, and CSM interaction has difficulties accounting for the precursor
plateau self-consistently. Radioactive decay is less likely to be the mechanism
that powers the luminosity. The host galaxy, detected in deep imaging with the
10 m GTC, is a moderately young and star-forming, but not a starburst, galaxy.
It has an absolute magnitude of M_g = -16.9.

Solar and Stellar Astrophysics