Iron line in the afterglow: a key to the progenitor
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The discovery of a powerful and transient iron line feature in the X-ray afterglow spectrum of GRB 970508 and GRB 970828, if confirmed, would be a major breakthrough for understanding the nature the progenitor of gamma-ray bursts. We show that a large mass of iron very close to the burster is necessary to produce the emission line. This in itself strongly limits the possible progenitor of the gamma-ray event, suggesting the former explosion of a supernova, as predicted in the Supranova model (Vietri & Stella 1998). The line emission process and the line intensity depend strongly on the age, density and temperature of the remnant. The simultaneous observation of the iron line and of a power-law optical afterglow lasted for one year strongly suggest that the burst emission is isotropic. Recent observations of GRB 990123 are also discussed.
8 pages, 1 postscript figure, proceedings of the workshop: "Gamma-Ray Bursts: the first three minutes", hald in Graftavallen (S), february 1999
8 pages, 1 postscript figure, proceedings of the workshop: "Gamma-Ray Bursts: the first three minutes", hald in Graftavallen (S), february 1999