When a supergiant finally goes bang it produces a massive burst of gamma rays and that burst lasts much longer because the supergiant is so big and there's much more fuel to burn through.

BBC: NASA's Swift satellite observes massive supernova stars

And that depends on being able to see the lower-energy radiation, in order to pinpoint what it was that exploded (gamma rays are impossible to focus, so the location of a burst is known only approximately).

ECONOMIST: Astronomy