Most interesting to me about Shibata-san's talk: low mass ratio neutron star binaries (~1, such as we see in our galaxy) will not produce an outflow if they produce a black hole after spiraling together due to gravitational wave radiation.
If we assume a black hole horizon is needed to produce a gamma ray burst (GRB), then this implies that the GRBs we see must involve a NS-BH inspiral, or a neutron star-neutron star inspiral of extreme mass ratio, but which nonetheless the masses add up to above the highest possible mass for a neutron star.
Inescapably, this implies that the neutron star binaries we see in our galaxy --- all of which have low mass ratios (~1) -- do not produce the observed gamma ray bursts.
Thus, the gamma ray burst rate is due to binaries which we have not yet observed in our own galaxy.
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