[vsnet-grb-info 3463] GRB 060707: OA fading and redshift

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5298
SUBJECT: GRB 060707: OA fading and redshift
DATE:    06/07/09 19:05:24 GMT
FROM:    Pall Jakobsson at U Hertfordshire  <palli at star.herts.ac.uk>

Pall Jakobsson, Nial Tanvir (Univ. of Hertfordshire), Brian L. Jensen,
Johan P. U. Fynbo (DARK, NBI), Antonio de Ugarte Postigo, Javier
Gorosabel (IAA-CSIC Granada), Sylvio Klose (TLS Tautenburg) and Paul
Vreeswijk (ESO) report on behalf of a larger collaboration:

Using FORS1 on the Very Large Telescope, we have obtained 3*30 min
spectra (300V) of the GRB 060707 field (Moretti et al., GCN 5285). The
acquisition image shows that the proposed optical afterglow (de Ugarte
Postigo et al., GCN 5290) has faded by approximately two magnitudes.
Using photometric zeropoints from the ESO webpages we estimate the
afterglow magnitude to be R ~ 22.4 on July 9.329 (1.432 days post-burst).

The combined spectrum displays a strong absorption feature around
5386 AA, with the flux dropping substantially blueward of this feature.
Associating it with Ly-alpha gives a redshift of z = 3.43 for the burst.
At this redshift we find several other absorption features, including
Ly-beta, Si II, Si IV, C IV, Al II and O III].