[vsnet-grb-info 3867] GRB 061004: Optical afterglow candidate and redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5698
SUBJECT: GRB 061004: Optical afterglow candidate and redshift
DATE:    06/10/05 21:08:41 GMT
FROM:    Pall Jakobsson at U Hertfordshire  <palli at star.herts.ac.uk>

Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo,
Brian L. Jensen , Jens Hjorth (DARK, NBI), Andrew Levan
(U. Hertfordshire), Nial Tanvir (U. Leicester), Paul Vreeswijk
and Cedric Ledoux (ESO) report on behalf of a larger collaboration:

Using FORS1 on the Very Large Telescope, we have imaged the
GRB 061004 field (Ziaeepour et al. GCN 5691) on Oct 5.369
(0.542 days post-burst). Inside the revised XRT circle (Page
et al. GCN 5695) we find an R ~ 23 mag point source, using
photometric zeropoints from the ESO webpages. At present
we cannot confirm that the source is fading. Its coordinates are:

R.A.(J2000) =  06:31:10.71
Dec(J2000)  = -45:54:28.7

with a 0.3" error in each coordinate.

We obtained a 30 min spectrum (300V grating) of this source
immediately after imaging. The spectrum displays an absorption
feature around 5230 A, with the flux dropping substantially blueward
of this feature. Associating it with Ly-alpha gives a redshift of
z ~ 3.3 for this proposed afterglow candidate.

A finding chart can be found at:
http://www.dark-cosmology.dk/~brian_j/grb/grb061004.827/

We thank the Paranal staff, especially Chris Lidman and Rachel
Gilmour for excellent support.