  Observational evidence for black hole spin down has been found in the
normalized light curves of long GRBs in the BATSE catalogue. Over the duration
$T_{90}$ of the burst, matter swept up by the central black hole is susceptible
to non-axisymmetries producing gravitational radiation with a negative chirp. A
time sliced matched filtering method is introduced to capture phase-coherence
on intermediate timescales, $\tau$, here tested by injection of templates into
experimental strain noise, $h_n(t)$. For TAMA 300, $h_n(f)\simeq 10^{-21}$
Hz$^{-\frac{1}{2}}$ at $f=1$ kHz gives a sensitivity distance for a reasonably
accurate extraction of the trajectory in the time frequency domain of about
$D\simeq 0.07-0.10$ Mpc for spin fown of black holes of mass $M=10-12M_\odot$
with $\tau=1$ s. Extrapolation to advanced detectors implies $D\simeq 35-50$
Mpc for $h_n(f)\simeq 2\times 10^{-24}$ Hz$^{-\frac{1}{2}}$ around 1 kHz, which
will open a new window to rigorous calorimetry on Kerr black holes.
