{
  "bibcode": "2006GCN..5782....1J",
  "body": "Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo,\nBrian L. Jensen , Jens Hjorth, Maximilian D. Stritzinger\n(DARK, NBI), Andrew Levan (U. Hertfordshire), Nial Tanvir\n(U. Leicester), Paul Vreeswijk, Cedric Ledoux (ESO),\nHouri Ziaeepour (UCL-MSSL) and Mathew Smith (U. Portsmouth)\nreport on behalf of a larger collaboration:\n\nWe have performed follow-up observations of the GRB 061004\noptical afterglow candidate (S1) reported in Jakobsson et al.\n(GCN 5698). The S1 flux is roughly constant between the\nthree epochs of observations:\n\n\nTel/inst   Date (UT)    Delta-t   Exp. time     Magnitude\n                         (days)    (s)\n--------------------------------------------------------------\nVLT/FORS1  Oct  5.366    0.539    2*300         22.55 +/- 0.09\nVLT/FORS1  Oct  7.344    2.517    2*300 + 120   22.82 +/- 0.07\nNTT/EMMI   Oct 15.352   10.525    3*500         22.73 +/- 0.20\n\n\nIn addition, S1 is 3.9\" from the edge of the revised XRT error\ncircle (Racusin et al. GCN 5774). The most likely conclusion\nis that S1 is not associated with the GRB.\n\nThere is no evidence for other sources inside the revised XRT\nerror circle. The limiting magnitude of our first epoch\nobservation is R > 25.1 (2 sigma). The corresponding upper limit\non beta_OX is 0.42, rendering the burst dark according to the\ndefinition proposed by Jakobsson et al. (2004, ApJ, 617, L21).\n\nConsidering the brightness of S1, it is unlikely that it is a\nnormal galaxy if z ~ 3.3 (GCN 5698). The relatively low S/N of\nthe VLT spectrum makes it difficult to reach a firm conclusion\non the reality of absorption features (apart from the feature\naround 5230 A). The lack of broad emission lines and the\nmarginal evidence for optical variability might indicate that\nS1 is a blazar. An alternative scenario is that S1 is at a lower\nredshift. The 5230 A feature could be the Balmer/4000 A break,\nindicating a redshift of z ~ 0.3.\n\nWe thank Kim Page for providing us with the afterglow X-ray flux.",
  "circularId": 5782,
  "createdOn": 1162474464000,
  "email": "P.Jakobsson@herts.ac.uk",
  "subject": "GRB 061004: Further VLT/NTT observations",
  "submitter": "Pall Jakobsson at U Hertfordshire  <P.Jakobsson@herts.ac.uk>",
  "eventId": "GRB 061004"
}