TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  747
SUBJECT: GRB 000630: Detection of the Optical Afterglow
DATE:    00/07/04 01:28:10 GMT
FROM:    Brian Lindgren Jensen at U.of Copenhagen  <brian_j@astro.ku.dk>

B. L. Jensen, J. P. U. Fynbo, H. Pedersen, J. Hjorth (U. of Copenhagen),
J. Gorosabel (DSRI, Copenhagen), D. G. Delgado (Stockholm Observatory), 
H. Schwarz (NOT) and A. Henden (USRA/USNO) report:

"We present further R-band observations of the IPN errorbox of GRB 000630
(Hurley et al. GCN #736) obtained with the NOT 2.56-m and the USNOFS 1.0-m. 
Comparison of three new epochs with our June 30.9 NOT observations (GCN #739) 
reveals a single transient object (less than an arcmin from the center of the 
IPN error box) which has faded monotonicly from 21 hours to 94 hours after the 
burst. The position of the point-like object, which we identify as the likely 
optical afterglow of GRB 000630, is RA(J2000) = 14:47:13.49, Dec(J2000) = 
+41:13:53.3, with an astrometric uncertainty of 0.7" relative to the USNO-A2.0 
catalog. Based on the photometric calibration of Henden (GCN #746) we find 
the following magnitudes for the optical afterglow using PSF photometry: 

      Date 2000 UT   Telescope    Exp. time   FWHM  t_burst+     R (mag)

      June 30.9      NOT 2.56-m   3x300 s     0.9"    21 h     23.04+-0.08
      July  1.3      USNO 1.0-m  18x600 s     2.1"    29 h     23.13+-0.25
      July  1.9      NOT 2.56-m   3x600 s     1.2"    46 h     24.05+-0.16
      July  3.9      NOT 2.56-m   5x600 s     0.8"    94 h     24.70+-0.16

The lightcurve resulting from these data points is consistent with a power-law 
decay with an index of -1.1 +- 0.3, assuming no contribution from an 
underlying host galaxy. We note that the burst occurred in a region with an 
apparent overdensity of galaxies. Sections of the images and a lightcurve are 
posted at http://www.astro.ku.dk/~brian_j/grb/grb000630/ ."