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GCN Circular 260

GRB990123 observations
1999-02-19T13:42:03Z (25 years ago)
Christian Veillet at CFHT <>
Christian Veillet reports:

The optical transient (OT) associated with the gamma ray burst GRB990123
has been observed with the new wide field camera CFH12k at the prime focus
of the 3.6-m CFH Telescope for two additional nights on 1999 Feb. 8.6 and
9.6 by C. Veillet in the course of the French GRB follow-up program
at CFHT (M. Boer, CESR, C. Veillet, CFHT) with the assistance of
J. Anderson (University of Victoria - Canada), as a continuation
of the observations reported in GCN 253 from the three previous nights. 

Using only the last three nights (image quality better than 1 arc-second),
photometric measurements in B, V and R using the star #18  published by 
Nilakshi et al. (GCN 252) give the following results:

R = 23.41 (0.1)  on 1999 Feb. 8.6  - 130 mn total integration time
V = 24.05 (0.1)  on 1999 Feb. 8.6  -  50 mn total integration time
B = 24.46 (0.15) on 1999 Feb. 9.6  -  30 mn total integration time

The V magnitude is in good agreement with the HST estimate
of the OT+galaxy magnitude (V~24 GCN 255).

As suspected from the first published image based on the first three nights
(GCN 253) with the first two of poor image quality, the surrounding galaxy 
is now clearly resolved.  A composite image in R and contour maps
of the GRB area and of a nearby comparison star are available at the Web site 

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