The following is this writer's understanding, of the mechanism, by which a core-collapsing hyper-massive star generates, firstly, a central stellar-massed BH ('polar pancake phase'); and, secondly, a short-lived Accretion Disk, around that BH, whose 'consumption' powers the GRB jets, parallel to the rotation axis ('equatorial consumption phase'). Is such the conventional explanation ?

 

 

According to figure 10, from a redshift of z ~ 1, that which is observed to span 4 days, "here-and-now" at earth, actually occurred over only 2 days, "there-and-then", at the source, in the source-frame. Whilst Prof. Perlmutter is referring, in said cited source, to SNIa, surely the same "stretch factor" affects GRBs, as well. Perhaps this has some impact, on the "short-burst" vs. "long-burst" debate ?? All else being equal, more cosmologically distant GRB Hyper-Novae (HN) will appear to have longer, more slowly evolving, light-curves... could those durations be used, to estimate, the red-shift, of the source-emitter HN ???