GCN Circular 8914
Subject
GRB 081211B: Nearby cluster
Date
2009-02-23T05:25:22Z (15 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, J. S. Bloom, and N. R. Butler (UC Berkeley) report:
GRB 081211B was discovered in the Swift-BAT slew survey (Copete et al,
GCN 8661) and, based on observations by Konus-Wind (Golenetskii et al.,
GCN 8676), was classified as a possible short burst with an extended
emission component. We note that the GRB localization lies within a
visual galaxy overdensity in SDSS archival imaging, and near the centers
of several reported clusters in the literature, which likely correspond
to the same physically extended structure: ZW 3893, Abell 1196, and
MaxBCG J168.22310+53.83028.
Redshifts from the Sloan Digital Sky Survey of the brightest two
apparent cluster members place this cluster at a probable redshift of
z=0.216.
On the night of 2009-02-19 (UT) we observed the field with Keck I (+
LRIS) for an exposure time of 990 sec (g-band) and 870 sec (R-band)
simultaneously through thin cloud cover. No host galaxy underlying the
XRT position (Page et al., GCN 8666) is detected to approximately R >
25, g > 26 mag. The nearest catalogued objects are:
SDSS J111303.09+534953.8 g=21.26 r=20.26 i=20.03 (7" = 24 kpc)
SDSS J111304.73+534959.5 g=20.56 r=19.25 i=18.84 (16" = 56 kpc)
An additional very faint extended object is located 3" west of the
center of the XRT position, outside the 90% confidence error circle.
Images of the field (from our observations and from SDSS) are posted to:
http://lyra.berkeley.edu/~dperley/081211b/081211b_keck.png
http://lyra.berkeley.edu/~dperley/081211b/081211b_sdss.png
If the BAT detection represents extended emission from this event and no
fainter host galaxy is found, this would constitute an additional case
of a short GRB event with detected extended emission occurring without a
coincident host galaxy (after GRB 080503 - arXiv:0811.1044), as well as
an additional example of a short burst occurring within a galaxy cluster
(see also e.g. GRBs 050509B, 050813, 051210, 061201). The isotropic
gamma-ray energy release at the cluster redshift would be 7 x 10^49 erg
in the BAT bandpass, comparable to values measured for other short GRBs.
We encourage deeper observations of the field.
