GRB 061004: Optical afterglow candidate and redshift
 

Click for larger images


Finding chart for GRB 061004.827
Acquisition image from VLT+FORS1. The circle indicates the refined XRT localisation (Page et al., GCN #5695).
The lines indicate the position of the optical source.
The black spike is due to a bright (R~10) star 1.5' to the south. 


NUMBER:  5698
SUBJECT: GRB 061004: Optical afterglow candidate and redshift 
DATE:    06/10/05

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. "

 

Last updated on October 05, 2006, by Brian Lindgren Jensen