Iron line afterglows: General constraints

¹ Osservatorio Astronomico di Brera, Via Bianchi 46, I–23807 Merate (Lc), Italy
² Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I–20133 Milano, Italy

Received: 18 December 1998
Accepted: 26 March 1999

Abstract

The discovery of a powerful and transient iron line feature in the X–ray afterglow spectra of γ–ray bursts would be a major breakthrough for understanding the nature of their progenitors, strongly suggesting the presence of a large, iron rich, mass in the vicinity of the burst event. Model–independent limits to the size and the mass of the the iron line emitting region are derived and discussed. We also discuss how these results can be used to constrain the amount of beaming or anisotropy of the burst emission.