GCN Circular 324

P.M. Vreeswijk, T.J. Galama, E. Rol, B. Stappers (U. of Amsterdam),
E. Palazzi, E. Pian, N. Masetti, F. Frontera (ITESRE, CNR, Bologna),
J. van Paradijs (U. of Amsterdam and U. of Alabama in Huntsville),
C. Kouveliotou (USRA/MSFC) and H. Boehnhardt (ESO) report on behalf of
the Amsterdam/Huntsville and BeppoSAX GRB optical follow-up teams:

Three 10-min red grism and three 10-min blue grism low resolution
spectra covering 3300-11000 Angstrom, were taken of the optical
counterpart to GRB 990510 (Vreeswijk et al.; GCN #310) with the
European Southern Observatory (ESO) VLT-UT1 telescope, starting May
11.21 UT. We identified the following ultraviolet absorption lines: 
Fe II (2344 and 2600 Angstrom), Mg II (blend of 2796 and 2803). These
lines are redshifted by z = 1.619 +- 0.002 (this may be a lower limit
to the redshift of the GRB source). On the basis of this redshift we
also find some weaker features, such as Al III (1863), Cr II/Zn II
(2062), and Mg I (2852). No strong emission lines were detected.

Assuming isotropic emission, z = 1.619, H0 = 70 km/s/Mpc and
Omega0=0.3, we find a (> 20 keV) energy output of 1.4x10^{53} ergs,
based on the BATSE fluence (Kippen et al.; GCN #322).


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