TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1573
SUBJECT: GRB 021004: steepening of the optical decay slope
DATE:    02/10/05 03:22:46 GMT
FROM:    James Rhoads at STScI  <rhoads@stsci.edu>

M. Weidinger (U. of Aarhus), M. P. Egholm (NOT), J. P. U. Fynbo,
B. Thomsen (U. of Aarhus), Palle Moller (ESO), J. Hjorth,
H. Pedersen, P. Jakobsson, B. L. Jensen (U.  of Copenhagen)
report on behalf of a larger collaboration:

"We have observed the optical afterglow of GRB 021004 (GCN #1564,
1565, 1568) with the 2.56m Nordical Optical Telescope (NOT) on La
Palma between 20:17:31 UT and 23:55:35 UT on Oct 4 2002.

We find R band magnitudes for five epochs:
      UT       R
   20:17:31  18.14
   20:24:00  18.12
   21:48:20  18.32
   22:37:37  18.40
   23:55:35  18.68

The magnitudes are based on a preliminary photometric calibration.
The USNO star at RA=00:26:58.713, DEC=+18:56:56.61 (GCN #1564) is
found to have a magnitude of R=15.64.

These five observations indicate that a break in the light curve has
occurred. The current decay slope is alpha=1.32. A light curve is
available at:
http://astro.phys.au.dk/~michaelw/GRB021004/lightcurve.ps
Here we have included the observations from GCN #1564, 1566, 1567 and
1570 assuming R=15.64 for the USNO star.

We also have obtained polarimetric observations and a spectrum
covering 3800AA-6800AA. From the lack of Ly-alpha absorption we
conclude that z<2.1."