  Multi-messenger emissions from SN1987A and GW170817/GRB170817A suggest a
Universe rife with multi-messenger transients associated with black holes and
neutron stars. For LIGO-Virgo, soon to be joined by KAGRA, these observations
promise unprecedented opportunities to probe the central engines of
core-collapse supernovae (CC-SNe) and gamma-ray bursts. Compared to neutron
stars, central engines powered by black hole-disk or torus systems may be of
particular interest to multi-messenger observations by the relatively large
energy reservoir $E_J$ of angular momentum, up to 29\% of total mass in the
Kerr metric. These central engines are expected from relatively massive stellar
progenitors and compact binary coalescence involving a neutron star. We review
prospects of multi-messenger emission by catalytic conversion of $E_J$ by a
non-axisymmetric disk or torus. Observational support for this radiation
process is found in a recent identification of ${\cal E}\simeq
(3.5\pm1)\%M_\odot c^2$ in Extended Emission to GW170817 at a significance of
4.2\,$\sigma$ concurrent with GRB170817A. A prospect on similar emissions from
nearby CC-SNe justifies the need for all-sky blind searches of long duration
bursts by heterogeneous computing.
