TITLE:   GCN CIRCULAR
NUMBER:  13332
SUBJECT: GRB 120521C: Keck Observations 
DATE:    12/05/22 12:59:03 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

D. A. Perley (Caltech), O. Yaron (Weizmann), Y. Cao, and S. R. Kulkarni
(Caltech) report:

We observed the position of GRB 120521C (Baumgartner et al., GCN 13318)
with the Keck I 10m telescope (+LRIS) starting at 10:39 UT on 2012-05-22.
We acquired a total of 1200s of imaging in I-band and 1360s in g-band.
Seeing conditions were relatively poor (1.5").

At the position of the enhanced XRT error circle (Beardmore et al., GCN
13324) we clearly identify a extended source in both the g-band and I-band
images.  It appears to consist of at least two components; a red source at
the southern edge of the XRT error circle and a bluer source at the
western edge of the error circle.  The relation of these sources to each
other and to GRB 120521C is not yet clear, but they could represent a
host-galaxy merger system, an afterglow superposed on a host, or two
unrelated galaxies at different redshifts.

The early nondetections of an afterglow (e.g. Klotz et al., GCN 13319;
Bersier et al., GCN 13320; De Cia et al., GCN 13321;
Levan et al., GCN 13322; Jelinek et al., GCN 13323; Morgan et al.,
GCN 13325; Gorbovskoy et al., GCN 13329; Oates et al., GCN 13331) are
characteristic of a dark burst.  Further observations of this event (in
particular in the NIR) are encouraged.

An image of the field is posted to:
http://www.astro.caltech.edu/~dperley/gcn/120521c/120521c.png