Beaming, Baryon-Loading, and the Synchrotron Self-Compton Component in Gamma-Ray Burst Blast Waves Energized by External Shocks

W e present detailed calculations ofnontherm alsynchrotron and synchrotron self-Com pton (SSC)spectra radiated by blastwavesthatareenergized by interactionswith a uniform surrounding m edium .Radio,optical,X -ray and gam m a-ray lightcurvesand spectralindicesarecalculated forastandard param etersetthatyieldshard G RB spectra during the prom pt em ission phase. Because no lateralspreading ofthe blast-wave is assum ed,the calculated tem poralbreaks represent the sharpest breaks possible from collim ated out(cid:13)ows in a uniform surrounding m edium . A bsence ofSSC hardenings in observed G RB X -ray afterglowsindicatesm agnetic(cid:12)eld generation toward equipartition as the blast wave evolves. EG RET detections of 100 M eV {G eV photons observed prom ptly and 90 m inutesafter G RB 940217 are attributed to nontherm alsynchrotron radiation and SSC em ission from a decelerating blast wave, respectively. The SSC process willproduce prom pt TeV em ission that could be observed from G RBs with redshifts z < (cid:24) 0 : 1,provided (cid:13) - (cid:13) opacity in thesourceissm all.M easurem entsofthetim e dependence of the 100 M eV -G eV spectralindices with the planned G LA ST m ission willchart the evolution ofthe SSC com ponent