Estimating the Prompt Electromagnetic Luminosity of a Black Hole Merger
  Although recent work in numerical relativity has made tremendous strides in
quantifying the gravitational wave luminosity of black hole mergers, very
little is known about the electromagnetic luminosity that might occur in
immediate conjunction with these events. We show that whenever the heat
deposited in the gas near a pair of merging black holes is proportional to its
total mass, and the surface density of the gas in the immediate vicinity is
greater than the (quite small) amount necessary to make it optically thick, the
characteristic scale of the luminosity emitted in direct association with the
merger is the Eddington luminosity independent of the gas mass. The duration of
the photon signal is proportional to the gas mass, and is generally rather
longer than the merger event. At somewhat larger distances, dissipation
associated with realigning the gas orbits to the new spin orientation of the
black hole can supplement dissipation of the energy gained from orbital
adjustment to the mass lost in gravitational radiation; these two heat sources
can combine to augment the electromagnetic radiation over longer timescales.
