Early X-Ray/Ultraviolet Line Signatures of Gamma-Ray Burst Progenitors and Hypernovae

We calculate the X-ray/UV spectral line signatures expected from theinteraction of a gamma-ray burst afterglow and a dense pre-burst environmentproduced by the progenitor. We explore the conditions under which Fe line andedge equivalent widths of $\sim$ 1 keV can arise, and discuss the possibilityof gaining information about possible progenitor scenarios using X-ray metalline spectra in the first few days of a burst. A wind or supernova shell aroundthe burst produces an X-ray absorption line spectrum and later emission lines,while a hypernova funnel model produces mainly emission lines. The Fe \ked canin some cases be more prominent than the Fe \kal line. Under simple assumptionsfor the input continuum luminosity, current reports of observed Fe lineluminosities are compatible with an Fe-enriched funnel model, while lowervalues are expected in shell models.Comment: revisions to ApJ ms first submitted 8/21/99; uses a higher and flatter input spectrum, with modified implications suggesting preference for funnel model