3 Search of Fe line in other GRB's afterglows

An extensive analysis is under way to search for features in all the X-ray afterglows observed by BeppoSAX. We report here the results derived in relatively bright afterglow sources (flux in the first part of the observation $\gt 3\ 10^{-13}\ \rm erg\ \rm cm2\ \rm s1$) which have a spectroscopic redshift determination, thus allowing to fix the energy of the line. In the two GRB's that meet these conditions (GRB 971214 and GRB 980613) we find upper limits that are roughly consistent with the intensity measured in GRB 970508 (Table 1).

  

Table 1: Iron lines in X-ray afterglows of GRB with known z

Note: Continuum and line intensities in the period $T_{\rm start}$ to $T_{\rm start}$+ 30 ksec; Errors and upper limits correspond to 90% confidence level for 1 parameter of interest; z of GRB 971214 from Kulkarni et al. (1998); z of GRB 980613 from Djorgovski et al. (1999). ¹ observation start in hrs from the GRB; $^2F(2-10~{\rm keV}$) in $10^{-13}\ \rm erg\ \rm cm2\ \rm s1$;³ Line intensity in 10^-5 ph cm^-2 s^-1; ⁴ observed E.W. in keV.