TITLE: GCN CIRCULAR NUMBER: 830 SUBJECT: GRB000926 - Optical observations DATE: 00/10/04 05:10:14 GMT FROM: Christian Veillet at CFHT Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit GRB000926 - Optical observations The optical counterpart of GRB000926 has been observed using the CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH Telescope for the fifth night on Oct. 3.2304 . Following GCN #829 by Halpern et al., a more accurate reduction of the CFHT data has been made, with the problems encountered when none of the observations is made in photometric reduction. A fist full reduction of the images leads to a more constant slope. The change seen previously in the decay rate (GCN #825, #826 and #827) doesn't seem to be real. Even if there are still discrepancies between the MDM and CFHT data, there are now smaller, thanks to the work on the secondary reference stars made by F. Vrba (USNO). The 5 nights of observations at CFHT lead to a decay slope of 2.16 +/- 0.03 but it's not really possible to link accurately the CFHT magnitudes to others as long as there is no calibration of the field stars made. A graph of the light curve in R from CFHT observations can be found at http://www.cfht.hawaii.edu/~veillet/grb.html where more information on the photometric reductions can be found. An accurate photometric calibration of stars 1 and 2 (see the image on the web page) is definitely needed. L. Wells, D. Woodworth and J. Luthe are acknowledged for their help in this observation. This message may be cited. -- ************************************************************ Dr. Christian Veillet, CFHT Senior Resident Astronomer Phone: (808) 885-3161 http://www.cfht.hawaii.edu/~veillet/ ************************************************************