TITLE: GCN CIRCULAR NUMBER: 5782 SUBJECT: GRB 061004: Further VLT/NTT observations DATE: 06/11/02 13:34:24 GMT FROM: Pall Jakobsson at U Hertfordshire Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo, Brian L. Jensen , Jens Hjorth, Maximilian D. Stritzinger (DARK, NBI), Andrew Levan (U. Hertfordshire), Nial Tanvir (U. Leicester), Paul Vreeswijk, Cedric Ledoux (ESO), Houri Ziaeepour (UCL-MSSL) and Mathew Smith (U. Portsmouth) report on behalf of a larger collaboration: We have performed follow-up observations of the GRB 061004 optical afterglow candidate (S1) reported in Jakobsson et al. (GCN 5698). The S1 flux is roughly constant between the three epochs of observations: Tel/inst Date (UT) Delta-t Exp. time Magnitude (days) (s) -------------------------------------------------------------- VLT/FORS1 Oct 5.366 0.539 2*300 22.55 +/- 0.09 VLT/FORS1 Oct 7.344 2.517 2*300 + 120 22.82 +/- 0.07 NTT/EMMI Oct 15.352 10.525 3*500 22.73 +/- 0.20 In addition, S1 is 3.9" from the edge of the revised XRT error circle (Racusin et al. GCN 5774). The most likely conclusion is that S1 is not associated with the GRB. There is no evidence for other sources inside the revised XRT error circle. The limiting magnitude of our first epoch observation is R > 25.1 (2 sigma). The corresponding upper limit on beta_OX is 0.42, rendering the burst dark according to the definition proposed by Jakobsson et al. (2004, ApJ, 617, L21). Considering the brightness of S1, it is unlikely that it is a normal galaxy if z ~ 3.3 (GCN 5698). The relatively low S/N of the VLT spectrum makes it difficult to reach a firm conclusion on the reality of absorption features (apart from the feature around 5230 A). The lack of broad emission lines and the marginal evidence for optical variability might indicate that S1 is a blazar. An alternative scenario is that S1 is at a lower redshift. The 5230 A feature could be the Balmer/4000 A break, indicating a redshift of z ~ 0.3. We thank Kim Page for providing us with the afterglow X-ray flux.