Precursor Plerionic Activity and High Energy Gamma-ray Emission in the Supranova Model of Gamma-ray Bursts

The supranova model of gamma-ray bursts (GRBs), in which the GRB event is preceded by a supernova (SN) explosion by a few months to years, has recently gained support from Fe line detections in the Xray afterglows of some GRBs. A crucial ingredient of this model yet to be studied is the fast-rotating pulsar that should be active during the time interval between the SN and the GRB, driving a powerful wind and a luminous plerionic nebula. We discuss some observational consequences of this precursor plerion, which should provide important tests for the supranova model: 1) the fragmentation of the outlying SN ejecta material by the plerion and its implications for Fe line emission; and 2) the effect of inverse Compton cooling and emission in the GRB external shock due to the plerion radiation field. The plerion-induced inverse Compton emission can dominate in the GeV-TeV energy range during the afterglow, being detectable by GLAST from redshifts z ∼< 1.5 and by AGILE from redshifts z ∼< 0.5, and distinguishable from self-Compton emission by its spectrum and light curve. The prospects for direct detection and identification of the precursor plerion emission are also briefly considered. Subject headings: gamma rays: bursts, pulsars: general, stars: neutron, supernova remnants, radiation mechanisms: non-thermal, line: formation