[vsnet-grb-info 1959] GRB 050813: Magellan detection of a high
redshift galaxy cluster
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Sun Aug 14 14:30:59 JST 2005
TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 3798
SUBJECT: GRB 050813: Magellan detection of a high redshift galaxy cluster
DATE: 05/08/14 05:28:50 GMT
FROM: Edo Berger at Carnegie Obs <eberger at ociw.edu>
Mike Gladders, Edo Berger (Carnegie Observatories), Nidia Morrell, and
Miguel Roth (Las Campanas Observatory) report:
"We imaged the field of GRB 050813 (GCN 3788) with the PANIC IR camera on
the Magellan/Baade 6.5-m telescope starting on 2005 Aug. 14.017 UT.
Observations were obtained with the K-s and Y-Carnegie filters, under poor
conditions (variable thick clouds, bright moonlight, and poor seeing of
~1"). Initial processing of these data suggest that this line of sight is
centered on a high-redshift galaxy cluster. A composite Y-K color image,
as well as a greyscale image of the stacked K frame is shown at:
http://www.ociw.edu:/~eberger/grb050813_panic.jpg
The apparent centrally concentrated population of faint galaxies with red
and uniform colors is strongly suggestive of a galaxy cluster, and looks
similar to extensive data taken with this instrument on known high-z
galaxy clusters from the Red-Sequence Cluster Survey (Gladders & Yee
2005). The apparent size of the core of this distribution (~1 arcmin) and
the magnitude of the objects suggest this putative cluster is at high
redshift (above z=0.5, and likely at z~1). The objects noted as B and C by
Gorosabel et al. (GCN 3796) in the XRT error circle are both red and
likely cluster ellipticals, and both are approximately K=19, based on an
initial calibration of the image to the 2MASS magnitude of the bright star
to the immediate SE of these objects.
Given the low probability of a chance coincidence we suggest that GRB
050813 most likely occurred in the cluster environment. This supports
recent associations of short GRBs with old galaxies (050509b: Bloom et al.
astro-ph/0505480; 050724: Berger et al. astro-ph/0508115). The likely
higher redshift compared to the latter two events may also explain the
faintness of the X-ray afterglow (GCN 3790)."
Further observations are planned.
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