In the article, the author states that the observed supernova was “one of only a handful . . . heralded by a burst of gamma rays.” Isn’t that because gamma-ray bursts from core-collapse supernovas are directional, along the axis of rotation? Was GRB 060218 “unique” because it produced a burst of gamma rays or because its axis was pointed our way?

Peter Wilson
Simi Valley, Calif.

Gamma-ray bursts are directional, but less than 1 percent of supernovas are associated with gamma-ray bursts. Moreover, the supernovas are fainter, and therefore harder to detect, than gamma-ray bursts. That’s why only a few of these supernovas have been detected .—R. Cowen