GCN Circular 1324

GRB011212: Optical Observations

A. Dullighan, G. Monnelly, G. Ricker, R. Vanderspek, N. Morgan (MIT);
and D. Tholen (U.Hawaii)

write:

We have observed the error box of the HETE GRB011212 (GCN #1194
Not found
 
 
) with
the Baade 6.5m telescope at Magellan on 2001 December 14.17 UT (Epoch
1) and December 15.17 UT (Epoch 2) using the MagIC CCD detector.
Twelve 360s R-band exposures were used to mosaic the entire HETE and
RXTE/ASM joint error box on each night.  Both nights had a seeing of
0.7" with a limiting magnitude of 24.5, except for the last half of
the second night when the seeing decreased slowly to 1.3", with a
limiting magnitude of 24.0 on the last frame.  Third epoch
observations were made with the University of Hawaii 2.2m telescope on
Mauna Kea on 2002 February 16.33 and 17.38 UT.  Three frames were used
to mosaic the error box each with three 600s VR-band exposures under
conditions of 1.3" seeing, giving a limiting magnitude of 24.5 after
summing.

Aperture photometry was performed on all objects detected in the
Epoch 1 images and then again at the same positions in the later
epochs.  The absolute magnitude of each source was calculated using a
nearby USNO catalog star: for each source, the same calibration star
was used in all epochs, and the quoted error in the magnitude does not
include the uncertainty in the magnitude of the calibration star.
Comparison with Epoch 3 is complicated by the fact that it is in
VR-band, whereas Epochs 1 and 2 are in R-band.  Four sources were
determined to have faded between both Epochs 1 and 2 and between
Epochs 1 and 3.  Their positions and magnitudes are listed below.
Sources 2, 3, and 4 faded to near the detection limit in Epoch 2, and
to below the detection limit in Epoch 3.  The observed fading and
upper limits are consistent with a temporal power law decay index
between -1 and -2, except for source 1 in Epoch 3, but this flattening
of the decay could be due to an underlying galaxy.

grb event: 2001 December 12.1695 UT
Epoch 1:   2001 December 14.17	2.0 days after
Epoch 2:   2001 December 15.17 	3.0 days
Epoch 3:   2002 February 16.33 	66.2 days
            2002 February 17.38 	67.2 days

Fading Sources
     RA       Dec        Epoch 1 m(R)    Epoch 2 m(R)     Epoch 3 m(VR)
1  4:59:58.1 +32:02:57  23.14 +/- 0.12  23.89 +/- 0.22   24.08 +/-0.24
2  4:59:59.4 +32:03:43  23.80 +/- 0.18  24.65 +/- 0.39    > 24.5
3  4:59:59.0 +32:09:04  23.75 +/- 0.18  24.80 +/- 0.48    > 24.5
4  4:59:39.5 +32:08:34  23.38 +/- 0.12  24.41 +/- 0.38    > 24.5

Finder charts have been prepared of the four sources from the Epoch 1
observations at http://space.mit.edu/HETE/Bursts/GRB011212.  The
charts contain the source, marked by crosshairs, a bright star (B)
from the USNO catalogue, and a constant star (C) of comparible
magnitude to the source.  The charts have a width and height of 33
arcseconds in RA and Dec.  North is up and East is to the left.

Source#    m(R)               Star B m(R)	 Star C m(R)
  1         23.14 +/- 0.12     18.8(USNO)	 23.65 +/- 0.15
  2         23.80 +/- 0.18     16.9(USNO)	 23.59 +/- 0.15
  3         23.75 +/- 0.18     14.4(USNO)	 23.48 +/- 0.14
  4         23.38 +/- 0.12     16.8(USNO)	 23.11 +/- 0.09


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