ON FUELING GAMMA-RAY BURSTS AND THEIR AFTERGLOWS WITH PULSARS

Gamma-ray bursts (GRBs) and their afterglows seem to result from the d issipation of bulk energy in relativistic outflows, but their engine h as not been identified. The engine could be a young pulsar formed from accretion-induced collapse with a dynamo-amplified magnetic field. El sewhere, we suggest that such strong field (cosmological) pulsars may help to explain the bimodal GRB duration distribution. Here we discuss the possible roles of a pulsar for the afterglow. We derive the expec ted bolometric luminosity decay and emphasize that the extracted rotat ional energy could dissipate by shocks and/or by large-amplitude elect romagnetic waves (LAEMWs). The simplest LAEMW approach predicts a slow er decay in the observed afterglow peak frequency and a faster decay i n the flux than the simplest blast wave, although more complicated mod els of both can produce different dependences. LAEMWs do not require t he rapid magnetic field amplification demanded of the blast-wave appro ach because the emission originates from a nearly fixed radius. Differ ent time evolution of GRB and post-GRB emission is also predicted. Evi dence for a pulsar in a GRB would make some GRB engine models, such as neutron star mergers and black holes, unlikely. Thus, the question of a pulsar presence is important even if it could drive a canonical fir eball.