  We present theoretical predictions for the spectral, temporal and intensity
signatures of the electromagnetic radiation emitted during the process of the
gravitational collapse of a stellar core to a black hole, during which
electromagnetic field strengths rise over the critical value for $e^+e^-$ pair
creation. The last phases of this gravitational collapse are studied, leading
to the formation of a black hole with a subcritical electromagnetic field,
likely with zero charge, and an outgoing pulse of initially optically thick
$e^+e^-$-photon plasma. Such a pulse reaches transparency at Lorentz gamma
factors of $10^2$--$10^4$. We find a clear signature in the outgoing
electromagnetic signal, drifting from a soft to a hard spectrum, on very
precise time-scales and with a very specific intensity modulation. The
relevance of these theoretical results for the understanding of short gamma-ray
bursts is outlined.
