[vsnet-grb-info 450] GRB 021004: Optical Decay

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1593
SUBJECT: GRB 021004: Optical Decay
DATE:    02/10/06 21:11:14 GMT
FROM:    Jules Halpern at Columbia U.  <jules@astro.columbia.edu>

J. P. Halpern, N. Mirabal, E. K. Armstrong, C. C. Espaillat (Columbia),
J. Kemp (Joint Astronomy Centre and Columbia) report for the MDM GRB
follow-up team:

"Continued monitoring of the optical afterglow of GRB 021004 with
the MDM 1.3m yields the following measurements on On 2002 Oct 6 UT:

		--------------------
		  UT      R     +/-
		--------------------
		02:41	19.84	0.03
		07:03	19.91	0.02
		11:39	20.00	0.02
		--------------------

Here we used the revised calibration of Henden (GCN #1583) in which
the reference has star has R=15.52.  Previous R magnitudes reported
in GCN #1578 would have to be decreased by 0.12 to match this reference.
The mean R-band decay between 8 and 48 hours as determined by the NOT and
MDM measurements can be described as a power law of slope -1.05, but with
highly significant deviations from a power law (Winn et al., GCN #1576)
that are robust against cross-calibration issues."

An updated decay curve will be maintained at:

http://www.astro.columbia.edu/~jules/021004.ps

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