We report the possible detection ( 99.3 % of statistical significance ) of redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst GRB970508 observed by BeppoSAX .
Its energy is consistent with the redshift of the putative host galaxy determined from optical spectroscopy .
The line disappeared \sim 1 day after the burst .
We have also analyzed the spectral variability during the outburst event that characterizes the X-ray afterglow of this GRB .
The spectrum gets harder during the flare , turning to steep when the flux decreases .
The variability , intensity and width of the line indicate that the emitting region should have a mass \gtrsim 0.5 M _ { \odot } ( assuming the iron abundance similar to its solar value ) , a size of \sim 3 \times 10 ^ { 15 } cm , is distributed anisotropically , and is moving with sub-relativistic speed .
In contrast to the fairly clean environment expected in the merging of two neutron stars , the observed line properties would imply that the site of the burst is embedded in a large mass of material , consistent with pre-explosion ejecta of a very massive star .
This material could be related with the outburst observed in the afterglow 1 day after the GRB and with the spectral variations measured during this phase .