GCN Circular 3420
Subject
GRB050509b, Bok telescope B-band imaging
Date
2005-05-13T00:34:33Z (20 years ago)
From
Daniel Eisenstein at U of Arizona <deisenstein@as.arizona.edu>
Charles W. Engelbracht and Daniel J. Eisenstein (Arizona) report:
We acquired B-band imaging of the field of GRB050509b using the 90-prime
1-degree camera on the 2.3-m Bok telescope. The time of the observation
was 0500 UT May 10 (25 hours after the burst). The exposure time was 20
minutes, and the seeing was 1.7" due to wind shake. We clearly detect
the source S1 (GCN 3388, 3401) at a B-band magnitude of 23.9. We do
not find any sources in our B-band image that are not in the Hjorth et
al. JPG image (GCN 3410).
We are making the calibrated data for a 30' square region centered on
the burst available at
http://cmb.as.arizona.edu/~eisenste/grb050509b/grb050509b_B.fits.gz
The header contains WCS astrometric information, good to 0.5".
We estimate the photometric calibration at 5%. If you are using the B
band image, please send an email to deisenstein@as.arizona.edu so that
we can inform you of any revisions.
While this image is surely not as deep as the nearly contemporaneous
Keck LRIS imaging (GCN 3409), it may be useful for photometric redshifts.
The B band lies blueward of but close to the 4000A break for the cluster
at z=0.225 (Gal et al., AJ, 125, 2064, 2003; Prochaska et al., GCN 3399).
Combined with slightly redder filters (V or g), one should be able to
efficiently distinguish cluster members from higher redshift galaxies.
We remark that if the GRB is at a much higher redshift than the cluster,
then mapping of the cluster may be important for assessing the impact of
gravitational lensing on the interpretation the burst. The velocity
dispersion of 340 km/s (Prochaska et al., GCN 3399) for the large
galaxy near the XRT position (Rol et al., GCN 3395) would predict an
Einstein radius of 3.3" with a singular isothermal sphere model and an
infinitely distant source. The embedding of the galaxy in the cluster
may increase this value. Although multiple imaging remains unlikely,
there should be non-negligible magnification.
This note can be cited.