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GCN Circular 1776

Subject
GRB 021112: Evidence for Another Dark Optical Afterglow
Date
2002-12-22T00:16:58Z (21 years ago)
From
Melissa Nysewander at UNC,Chapel Hill <mnysewan@astro.unc.edu>
J. Schaefer, S. Savage, R. Canterna (U. Wyoming), M. Nysewander, D.
Reichart (U. North Carolina), A. Henden (USRA/USNO), and D. Lamb (U.
Chicago) report on behalf of a larger collaboration:

We observed the inner 93% of the 40-arcminute diameter error circle of GRB
021112 (GCN 1682) with the 0.6-meter Red Buttes Observatory telescope
beginning 1.8 hours (GCN 1685) and 13.9 days after the burst.  For the
first epoch observation, we integrated without filter for 1800 seconds per
pointing x four pointings.  For the second epoch observation, we integrated
without filter for 2700 seconds per pointing x four pointings.

Unfiltered magnitudes measured with our Apogee AP8P CCD best mimic Rc
magnitudes.  Using the image subtraction routine ISIS2 (Alard 2000), we
find no candidates to the limiting magnitude of our first epoch image,
which we measure to be Rc = 21.8 mag (3 sigma), 22.2 mag (2 sigma), and
23.0 mag (1 sigma) using the field calibration of Henden (GCN 1697).

We note that the Galactic extinction along this line of sight is
approximately A_Rc = 0.52 mag (Schlegel et al. 1998).

The candidate of Strolger et al. (GCNs 1684, 1696) sits outside of the
above fields.  In addition to the arguments presented by Nysewander et al.
(GCN 1701), its BVRcIcH spectral flux distribution and low Galactic
latitude suggest that it is a low-mass flare star.

Dismissing this candidate, this is the deepest non-detection of an optical
afterglow beginning within 2.6 hours of a burst (GCN 1699).

Alard, C. 2000, A&AS 114, 363
Schlegel, D., et al. 1998, ApJ, 500, 525
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