Observation of X-ray lines from a Gamma-Ray Burst (GRB991216): Evidence   of Moving Ejecta from the Progenitor
  We report on the discovery of two emission features observed in the X-ray spectrum of the afterglow of the gamma-ray burst (GRB) of 16 Dec. 1999 by the Chandra X-Ray Observatory. These features are identified with the Ly$_{\alpha}$ line and the narrow recombination continuum by hydrogenic ions of iron at a redshift $z=1.00\pm0.02$, providing an unambiguous measurement of the distance of a GRB. Line width and intensity imply that the progenitor of the GRB was a massive star system that ejected, before the GRB event, $\approx 0.01 \Ms$ of iron at a velocity $\approx 0.1 c$, probably by a supernova explosion. 
L. Piro, G. Garmire, M. Garcia, G. Stratta, E. Costa, M. Feroci, P.   Meszaros, M. Vietri, H. Bradt, D. Frail, F. Frontera, ...