I was bothered with this issue for quite some time....
The increased flux of neutrinos (11 of them in Japanese Kamiokande detector!!
) was detected couple of hours before the '87A supernova outburst in visible light, and this fits nicely into theoretical model of this type of supernova.
However, because of neutrino oscillation, it has to have some rest mass, about 1eV or so... and that implies neutrinos from '87A were traveling and reached us with speed less that c (slightly less... by how much?)
That means that the core collapse must have occurred earlier than observed (by timing the neutrino flux).
I wonder if anybody knows more about it?
Bojan