GRBs, but most agree that some kind of explosion is involved.

ECONOMIST: Astronomy

GRBs are distant events has probably also been settled.

ECONOMIST: A symphony in gamma major

The caveat for Swift is that it sees stars at the ends of their lives, and there has to be a question mark over whether the redshift 8-10 era would be sufficiently mature to produce GRBs.

BBC: NEWS | Science/Nature | Telescope looks to go to the edge

GRBs are smaller, closer eruptions.

ECONOMIST: A symphony in gamma major