The redshift and GRB971214

After the result of GRB970508 no more redshift has been measured on the GRB optical transient itself but 3 redshift have been measured of an host object overimposed to the transient itself. Of course while the association of the absorption features of GRB970508 provides an unambiguous lower limit to the distance, the association of the GRB to each individual host is less compelling. The probability of a random association is in average of the order of 1% even if data come from instruments used at the limit of sensitivity and to be compared with a relatively poor statistics. Since in more than 3/4 of the cases optical transient are associated to a (slightly) extended object the following list is very likely true. Ordering by the redshift:

• GRB970508: z=0.835
• GRB980703: z=0.964
• GRB980613: z=1.096
• GRB971214: z=3.418

The result on GRB971214 is the most impressive since, assuming an isotropic emission (no beaming), it corresponds to a significant fraction of a solar mass (around 0.3) converted into electromagnetic energy in the 40-700 keV band. The impact of this datum was high. Until that date the most popular model for the "central engine" was the merging of a Neutron Star-Neutron Star binary system. The energy of GRB971214 requires a beaming if the emission is originated in this way, but this makes unlikely the observed rate of GRBs. Moreover, the optical transients, when imaged at high resolution, are usually in the central regions of their nebular hosts while the expectation on runaway velocity of binary systems including a collapsed object, combined with the long time required for the merging, makes more likely a location external to the galaxy at the moment of the collapse.