Name : Toshio MURAKAMI Institute : E-mail : murakami@astro.isas.ac.jp TITLE : Gamma-Ray Burst Observations ABSTRACT : The observational results on GRBs can be explained by the so-called fireball models. However, the nature of the progenitor of GRBs is an unsettled issue. Merging of a binary neutron star system and the collapse of a massive star or a hypernova are the most popular models. Clear observational evidence can be gathered through measurements of the iron spectral feature, produced by the medium surrounding the GRB progenitor. ASCA, BeppoSAX and, most recently, Chandra have detected strong iron features in some of the GRBs. The reported iron features were strong, variable and somewhat broad. The iron features observed at 5.04 keV with ASCA can be understood considering a recombination-edge in non-equilibrium condition of a low electron temperature, which might be produced by burstout mechanism. The existence of the strong iron features is more consistent with a massive collapsar as a progenitor.