GCN Circular 1429

J. Gorosabel (IAA-CSIC Granada), J. Hjorth, B. L. Jensen, H. Pedersen,
P. Jakobsson (Univ. of Copenhagen), J. Fynbo (IFA Aarhus), 
M. I. Andersen (Univ. of Oulu), report:

 We have carried out optical observations of the GRB 020604 IPN error box
 (GCN 1417
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 ) with the 1.54 Danish Telescope (+DFOSC) on three epochs;
 June 8, 9 and 10. The observations were done following a mosaic as
 detailed below:

 =====================================================================
  Date UT         Filter   R.A.       Dec    Seeing Time since ExpTime 
  June 2002              (J2000)    (J2000)   (")   GRB (days)   (s)   
 ---------------------------------------------------------------------
  8.07874--8.11230   R  16:27:42.0 -29:48:43  1.2     3.50      4x600   
  8.11259--8.14516   R  16:28:39.8 -29:43:44  1.2     3.54      4x600   
  8.14642--8.16250   R  16:29:19.8 -29:39:44  1.1     3.56      2x600   
  8.16629--8.21525   R  16:28:01.7 -29:48:22  1.2     3.60      6x600** 
  8.21554--8.23159   R  16:27:18.4 -29:55:38  1.1     3.63      2x600   
  8.23186--8.23973   R  16:26:45.4 -29:52:52  1.0     3.64        600   
  8.27211--8.31829   I  16:28:01.7 -29:48:22  1.1     3.70      6x500** 
  8.32037--8.34111   I  16:28:39.8 -29:43:44  1.4     3.74      3x500   
  8.34216--8.36298   I  16:27:18.4 -29:55:38  1.8     3.76      3x500   
 ---------------------------------------------------------------------
  9.12684--9.21986   R  16:28:01.7 -29:48:22  1.1     4.58     10x600** 
  9.22098--9.26678   R  16:28:39.8 -29:43:44  1.2     4.65      4x600   
  9.27909--9.30354   R  16:27:18.4 -29:55:38  1.3     4.70      4x600   
  9.30392--9.31180   R  16:26:45.4 -29:52:52  1.3     4.72        600   
  9.31378--9.32165   R  16:27:42.0 -29:48:43  1.2     4.72        600   
  9.32416--9.33202   R  16:29:19.8 -29:39:44  1.5     4.74        600   
 ---------------------------------------------------------------------
 10.16572--10.24745  R  16:28:01.7 -29:48:22  1.0     5.61      6x900** 
 10.26606--10.30406  R  16:28:39.8 -29:43:44  1.3     5.69      3x900   
 10.30569--10.34051  R  16:27:18.4 -29:55:38  1.5     5.73      4x600   
 ---------------------------------------------------------------------
 ** Central part				   	              
 =====================================================================

 The first and the second epoch observations cover the whole error box, 
 whereas the third epoch images contain ~80% of it.

 A gif of the performed mosaic can be seen at:
 http://www.dsri.dk/~jgu/grb020604/FCs/grb020604.R.8-9.06.02.1.54D.gif

 The limiting magnitude depends on the error box position. For the central
 pointing (covering ~50% of the error box), the R-band limiting magnitude 
 (3 sigma) at the three epochs are R=24.5, R=24.7 and R=24.9. For the rest
 of the error box the limiting magnitude are R=23.8, R=23.6 and R=24.0,
 respectively. In the I-band the limiting magnitude ranges from I=22.5 to
 I=23.4.

 Albeit the severe Galactic extinction (AR=1.18, AI=0.86 mag), many
 extragalactic objects are detected in our images. Among the unsaturated
 objects, marginal variability (< 0.2 mag) is detected for 12 of them. 
 None of these objects shows flux variability consistent with a decay, as
 expected for an optical afterglow 3.5-5.7 days after the gamma ray event.