On Fueling Gamma-Ray Bursts and Their Afterglows with Pulsars

Abstract

Gamma-ray bursts (GRBs) and their afterglows seem to result from the dissipation of bulk energy in relativistic outflows, but their engine has not been identified. The engine could be a young pulsar formed from accretion-induced collapse with a dynamo-amplified magnetic field. Elsewhere, 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 expected bolometric luminosity decay and emphasize that the extracted rotational energy could dissipate by shocks and/or by large-amplitude electromagnetic waves (LAEMWs). The simplest LAEMW approach predicts a slower decay in the observed afterglow peak frequency and a faster decay in the flux than the simplest blast wave, although more complicated models of both can produce different dependences. LAEMWs do not require the rapid magnetic field amplification demanded of the blast-wave approach because the emission originates from a nearly fixed radius. Different time evolution of GRB and post-GRB emission is also predicted. Evidence 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 fireball.