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 ispreceded by a supernova (SN) explosion by a few months to years, has recentlygained support from Fe line detections in X-ray afterglows. A crucialingredient of this model yet to be studied is the fast-rotating pulsar thatshould be active during the time interval between the SN and the GRB, driving apowerful wind and a luminous plerionic nebula. We discuss some observationalconsequences of this precursor plerion, which should provide important testsfor the supranova model: 1) the fragmentation of the outlying SN ejectamaterial by the plerion and its implications for Fe line emission; and 2) theeffect of inverse Compton cooling and emission in the GRB external shock due tothe plerion radiation field. The plerion-induced inverse Compton emission candominate in the GeV-TeV energy range during the afterglow, being detectable byGLAST from redshifts $z \lesssim 1.5$ and distinguishable from self-Comptonemission by its spectrum and light curve. The prospects for direct detectionand identification of the precursor plerion emission are also brieflyconsidered.Comment: ApJ vol.583, in pres