GCN Circular 1513

Mike Gladders (Carnegie Observatories) and Pat Hall
(Princeton/Catolica) report: 

"A total of 37 images (16 in I, 10 in R, 11 in V) of the OT associated
with GRB020813 were acquired with the Baade 6.5m (Magellan I)
telescope and TEK5 camera on the night of August 13 UT, under
conditions of excellent seeing and transparency. A further 15 images
(5 in I, 4 each in BR and 2 in V) were acquired on the night of August
14 UT, under similar conditions, though with some possible cirrus.

"A preliminary analysis of these images yields the magnitudes below
for the OT associated with GRB020813. Magnitudes have been computed
differentially relative to approximately 20 stars straddling the
magnitude range of OT, located in the same field (2x2 arcminutes).
Internal uncertainties (estimated from residuals in the differential
corrections) are about 0.01 magnitudes on August 13 UT, and about 0.02
on August 14UT, and the systematic uncertainty in the calibration of
the zero-points is less than 0.05 magnitudes in most cases. The B-band
zero-point, established on August 14 UT, may be affected by light
cirrus on the science frames, and is questionable."


August 13 UT:
-------------

I-band:
-------
 UT	Magnitude
 5.7742 17.910
 5.8922 17.928
 6.6153 18.061
 6.7461 18.090
 6.7733 18.108
 6.7986 18.078
 6.8236 18.106
 6.8486 18.104
 7.0036 18.139
 7.2939 18.192
 7.4225 18.208
 7.5400 18.249
 7.5650 18.241
 7.5900 18.233
 7.6153 18.228
 7.6403 18.273

R-band:
-------
 UT	Magnitude
 6.7061 18.491
 6.9122 18.520
 6.9422 18.536
 7.1478 18.578
 7.1728 18.579
 7.1978 18.582
 7.2228 18.591
 7.3222 18.608
 7.3925 18.625
 7.5083 18.654

V-band:
-------
 UT	Magnitude
 6.6767 18.850
 6.8836 18.882
 6.9739 18.916
 7.0400 18.922
 7.0653 18.930
 7.0906 18.929
 7.1156 18.932
 7.2614 18.953
 7.3592 18.982
 7.4508 19.000
 7.4781 18.999



August 14 UT:
-------------

I-band:
-------
 UT	Magnitude
 1.0033 19.854
 1.0344 19.862
 1.0594 19.837
 1.0844 19.891
 1.1094 19.848

R-band:
-------
 UT	Magnitude
 1.2447 20.420
 1.2697 20.411
 1.2947 20.420
 1.3197 20.419

V-band:
-------
 UT	Magnitude
 1.3486 20.805
 1.3736 20.811

B-band:
-------
 UT	Magnitude
 1.1397 21.365
 1.1647 21.315
 1.1897 21.343
 1.2147 21.338