Gamma Ray Burst optical follow-up program
    C. Veillet (CFHT)  - M. Boer  (CESR)

GRB000604 observations

June 7   (posted on June 7)


GRB000604 - Optical observations

The field of GRB000604 has been observed using the CFH12K CCD mosaic
camera at the prime focus of the 3.6-m CFH Telescope in the course of
the French GRB follow-up  program at CFHT.

Two 600s exposures with moderate seeing (image quality between 0.9" and 1.0")
have been obtained on 2000 June 07.430 UTC (mean epoch).

Close to the location of the candidate proposed in GCN 690 (Leibowitz et al),
only a very faint source, visible on both frames, is unambiguously detected.
Its location is  15:35:54.22 +10:41:23.9 , and it is the only source within
a radius of 8" of the proposed candidate. Source A position is found as
15:35:52.64 +10:41:08.0 , in good agreement with the position posted in GCN 692.

A preliminary photometric reduction shows this source to be 3.9 +/- 0.2
magnitudes fainter in R than source A (GCN 690). Would it be the GCN 690
candidate, it would mean a ~3.5 drop in magnitude in slightly less than
0.7 day. It would then be visible on June 6.26 exposures by Diercks et
al (GCN 692).

In agreement with Diercks et al (GCN 692), I conclude that the GCN 690
candidate  is likely to be unrelated to GRB000604.

An image of the candidate area is posted at

Another pair of images is planned tonight to allow a search for variable
sources on the whole GRB000604 field and a final check on the GCN 690

Alain Doressoundiram is acknowledged for his help in this observation.

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