Universal Afterglow Of Supernovaless Gamma-Ray Bursts

The early-time afterglows of gamma-ray bursts (GRBs) not associated with a supernova (SN) explosion (SN-less GRBs) can be scaled down to a dimensionless, parameter-free universal behavior. This universal behavior is that expected from a pulsar wind nebula afterglow powered by the rotational energy loss of a newly born pulsar. Such SN-less GRBs include short-hard bursts produced by the merger of binary neutron stars and long bursts presumably produced by the accretion-induced collapse of neutron stars to quark stars in high-mass x-ray binaries, or in isolation due to energy and angular momentum loss.