3 AFTERGLOWS We can cheer ourselves up by recalling that it is more elevated to make predictions than to explain phenomena a posteriori. --Sir Martin J. Rees, Royal Astronomical Society Presidential Address 11 February 1994 Had Ray Klebesadel and his collaborators found convinc- ing evidence for a connection of a GRB to a supernova, the search for late-time emission after a given GRB would have been sharpened and honed from the outset. Instead,