2 Possible evidence of Fe line feature in GRB 970508

We have searched the X-ray spectrum of GRB 970508's afterglow for an iron line, located at the system's redhift (z = 0.835, Bloom et al. 1998); we found such a line with limited statistical significance ($99.3\%$) in the early part (first $16\; h$) of the afterglow; the line decreases in the later part of the observations ($\approx 1$ day after the burst) by at least a factor 2, enough to make it undetectable with current apparatus (Fig. 1). Simultaneously with the line disappearance, the X-ray flux both rises and hardens ($\alpha = 0.4\pm 0.6$, while $\alpha = 1.5\pm 0.6$ before the reburst), consistent with the appearance of a new shock. Then, at the end of the outburst, the spectrum steepens.