GCN Circular 5995
Subject
GRB 061201: Nearby Galaxy Cluster Abell 995 is at z=0.0865
Date
2007-01-04T23:39:54Z (18 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
E. Berger (Carnegie Observatories) reports:
"On December 21.06 UT we used LDSS3 on the Magellan/Clay 6.5-m telescope
to obtain spectra of nine apparent members of the galaxy cluster Abell 995
located 8.5 arcmin away from the position of the short GRB 061201 (GCN
5880). Three of these galaxies have been previously observed by Blondin
et al. leading to a proposed redshift of z~0.237 for the cluster (GCN
5944). Based on our spectra, which cover the range of about 4000-9500A,
we find instead the following redshifts for the nine cluster members:
Redshift RA Dec
--------------------------------------------
z=0.0866 22:09:43.735 -74:26:28.92
z=0.0877 22:09:37.067 -74:26:39.84 *(object B)
z=0.0873 22:09:05.248 -74:29:29.55 *(object D)
z=0.0849 22:09:51.790 -74:31:11.06 *(object A)
z=0.0843 22:08:34.675 -74:26:20.81
z=0.0864 22:09:40.015 -74:26:53.18
z=0.0866 22:09:48.052 -74:28:26.22
z=0.0876 22:09:25.530 -74:29:50.85
z=0.0872 22:09:32.120 -74:27:35.99
These redshifts are based on absorption features corresponding to CaII
H&K, G-band, Mg b, E-band, and Na D, as well as H-alpha emission in four
of the nine objects. We therefore conclude that the redshift of Abell 995
is z=0.0835. The previously claimed redshift of z~0.237 is likely based
on a mis-identification of the Na D feature at lambda_rest ~ 5893A as Mg b
at lambda_rest ~ 5174A.
At the correct redshift of the cluster, the projected offset of GRB 061201
is about 0.8 Mpc from the center of the cluster. To cover this distance
over a period of about 10 Gyr, the kick velocity would have to be >80
km/sec.
Finally, we re-iterate the presence of a z=0.111 galaxy about 17 arcsec
from the optical position of GRB 061201, corresponding to a significantly
smaller offset of about 34 kpc (GCN 5952)."
*Objects A,B,D refer to the designation in GCN 5944