2001ApJ...550L..43V

We consider models for the generation of the emission line recently discovered in the X-ray afterglow spectrum of several bursts and, especially, of GRB 991216 observed by Chandra. These observations suggest the presence of 0.1-1 M_☉ of iron in the vicinity of the bursts. We show that there are strong geometric and kinematic constraints on the line-emitting material. We discuss several classes of models, favoring one where the line photons are produced by reflection off the walls of a wide funnel of semiopening angle θ~45° excavated in a young (a few months old) supernova remnant made of ~10 M_☉ with radius 6x10¹⁵ cm and ~1 M_☉ of iron, providing strong support for the ``supranova'' model.