TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3911
SUBJECT: GRB 050904: TAROT optical limits
DATE:    05/09/04 07:23:23 GMT
FROM:    Alain Klotz at CESR-CNRS  <Alain.Klotz@free.fr>

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 050904 detected by SWIFT
(trigger 153514) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 86s after the GCN trigger.
The field had an elevation of 60 degrees above horizon
and weather conditions were good.

We detected no new source comparing our unfiltered images
with the USNO-B catalog.

 From the first frame we give an early limit:

Day : 2005-09-04
UT-start      UT-end      (sec since GRB)  Exp(s)  R-mag
01:53:10.33 - 01:54:08.33   86 -  101          15  >16.0

We co-added 13 first frames and no new source
is detected:

Day : 2005-09-04
UT-start      UT-end      (sec since GRB)  Exp(s)  R-mag
01:53:10.33 - 02:00:18.74   86 -  515         360  >18.5

Limiting magnitude was estimated with the nearby USNO-B1 stars.

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