  The super-luminous object ASASSN-15lh (SN2015L) is an extreme event with a
total energy $E_{rad}\simeq 1.1\times 10^{52}$ erg in black body radiation on
par with its kinetic energy $E_k$ in ejecta and a late time plateau in the UV,
that defies a nuclear origin. It likely presents a new explosion mechanism for
hydrogen-deprived supernovae. With no radio emission and no H-rich environment
we propose to identify $E_{rad}$ with dissipation of a baryon-poor outflow in
the optically thick remnant stellar envelope produced by a central engine. By
negligible time scales of light crossing and radiative cooling of the envelope,
SN2015L's light curve closely tracks the evolution of this engine. We here
model its light curve by the evolution of black hole spin, during angular
momentum loss in Alv\'en waves to matter at the Inner Most Stable Circular
Orbit (ISCO). The duration is determined by $\sigma=M_T/M$ of the torus mass
$M_T$ around the black hole of mass $M$: $\sigma\sim 10^{-7}$ and $\sigma\sim
10^{-2}$ for SN2015L and, respectively, a long GRB. The observed
electromagnetic radiation herein represents a minor output of the rotational
energy $E_{rot}$ of the black hole, while most is radiated unseen in
gravitational radiation. This model explains the high-mass slow-spin binary
progenitor of GWB150914, as the remnant of two CC-SNe in an intra-day binary of
two massive stars. This model rigorously predicts a change in magnitude $\Delta
m\simeq 1.15$ in the light curve post-peak, in agreement with the light curve
of SN2015L with no fine-tuning.
