On the anomalous X-ray afterglows of GRB 970508 and 970828

Recently, BeppoSAX and ASCA have observed an unusual resurgence of soft X-r ay emission during the afterglows of GRB 970508 and 970828, together with m arginal evidence for the existence of Fe lines in both objects. We consider the implications of the existence of a torus of iron-rich material surroun ding the sites of gamma-ray bursts, as would be expected in the supra-nova model; in particular, we show that the fireball will quickly hit this torus , and bring it to a temperature of approximate to 3 x 10(7) K. Bremsstrahlu ng emission from the heated-up torus will cause a resurgence of the soft X- ray emission with all expected characteristics (flux level, duration and sp ectral hardening with time) identical to those observed during the reburst. Also, thermal emission from the torus will account for the observed iron l ine flux. These events are also observable, for instance by new missions su ch as SWIFT, when beaming away from our line of sight makes us miss the mai n burst, as fast (soft) X-ray transients, with durations of approximate to 10(3) s and fluences of approximate to 10(-7) - 10(-4) erg cm(-2). This mod el provides evidence in favour of the supra-nova model for gamma-ray bursts .