TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4680
SUBJECT: GRB060203: WHT Z-band observations
DATE:    06/02/05 23:28:39 GMT
FROM:    Evert Rol at U.Leicester  <er45@star.le.ac.uk>

E. Rol (U. of Leicester), A. Levan (U. of Hertsfordshire), K. Wiersema
(U. of Amsterdam), P. Dobbie, D. Boyce (U. of Leicester), N. Tanvir
(U. of Hertsfordshire) report on behalf of a larger collabration:

We have observed the optical counterpart of GRB060203 (Malesani, GCN
4645) with the Auxiliary Port Imaging Camera on the William Herschel
Telescope. We obtained two epochs of observations in Z-band. Our
results of seeing-matched aperture photometry are tabulated below:

time since burst  exposure time    seeing    magnitude
    (hours)          (seconds)     (arcsec)

       4.0           5 x 240         0.8       19.75
      22.8           5 x 240         0.7       21.60

The statistical error on the magnitude is typically 0.01, while we
estimate the zeropoint calibration error to be 0.3 magnitudes.

We thus measure a decay for the optical counterpart of 1.85 +/- 0.01 
magnitude over 18.8 hours, with an average decay index of 0.98 +/- 0.01.