GCN Circular 1164
Subject
GRB 011121: J-band observations
Date
2001-11-29T23:13:15Z (23 years ago)
From
Saurabh Jha at Harvard-Smithsonian CfA <sjha@cfa.harvard.edu>
M. M. Phillips (Carnegie), K. Krisciunas (CTIO), P. M. Garnavich,
S. Holland (Notre Dame), S. Jha, K. Z. Stanek (Harvard-Smithsonian
CfA) and P. McCarthy (Carnegie) report:
We have observed the field of GRB 011121 with the 6.5m Magellan I
Baade telescope (+ IR imager) on UT 2001 Nov 29.3 for a total of
4320s in the Js passband with 0.5" seeing in the combined image.
A finder chart of the combined image is available at:
http://cfa-www.harvard.edu/cfa/oir/Research/GRB/.
The data have been calibrated via three IR standard stars also
observed over the course of the night, from the list of Persson et al.
(1998, AJ, 116, 2475). The Js passband is slightly narrower than the
standard J, but we make no color correction and adopt Js = J because
we lack sufficient data (both for the standard stars and the objects
in the GRB field). The effects of the slight filter mismatch are
expected to be small (see, for example, Krisciunas et al. 2001, AJ,
122, 1616). For the bright stars marked in the finder, we measure J =
17.82 +/- 0.03 (star D) and J = 18.59 +/- 0.03 (star E).
A source at the position of the GRB afterglow is marginally detected,
but because of its faintness, it is difficult to separate a possible
point source from the underlying fuzz. Differential PSF-fitting
photometry relative to the bright stars in the field yields J = 21.9
+/- 0.1 for the source at the position of the GRB afterglow. Because
of the marginal detection, this should be viewed as an upper limit.
Two other sources are detected near the GRB position. One bright
source is located 0.8"S and 2.0"E of the GRB with J = 19.98 +/- 0.04.
This object may be the core of the GRB host galaxy, but it is not
clearly resolved -- it might be a foreground star. The other source
(the "blob") located 1.6"S and 2.6" E of the GRB is clearly detected
at J = 21.57 +/- 0.07, and is possibly extended.
Adopting J ~ 16 mag for the GRB afterglow on Nov 22.36 (GCN 1153), the
reported optical decay slope (GCN 1160) would predict J ~ 21 for the
afterglow at the time of these observations.
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