[vsnet-grb-info 1860] GRB 050724: Secure Host Redshift from Keck

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3700
SUBJECT: GRB 050724: Secure Host Redshift from Keck
DATE:    05/07/29 18:13:53 GMT
FROM:    Jason Prochaska at UCO/Lick Obs  <xavier at ucolick.org>

J. X. Prochaska (UCO/Lick), J. S. Bloom (UCB), H.-W. Chen (MIT),
B. Hansen (UCLA), J. Kalirai (UCSC), M. Rich (UCLA) and H. Richer (UBC)
report on behalf of the GRAASP collaboration:

"We have obtained LRISb spectroscopy (900s; 2005-07-29 06:31 UT)
of the putative host galaxy of GRB 050724 (Object D in GCN #3672).
We confirm our previously reported redshift (GCN #3679)
based on the identification of Ca H+K, G-band absorption features,
and the 4000Ang break.  We report a redshift z=0.258 +/- 0.002.
The velocity dispersion based on CaK appears to exceed 200km/s.
The galaxy shows no [OII] emission in our spectrum suggesting minimal
current star formation.

PAIRITEL imaging of the galaxy from July 29 UT yields a K-band magnitude
of 15.3 +/- 0.2 in a 3" radius aperture.  At this redshift,
and including the effects of Galactic extinction, the galaxy
is 1.7 L* based off the 2MASS luminosity function.

The properties of this galaxy -- a massive early-type at
moderate redshift -- are strikingly similar to the probable host
galaxy of GRB 050509b (GCN #3399).

Based on this redshift and the reported fluence in GCN #3667,
the isotropic -equivalent energy release is
E_gamma(iso) = 9.9e49 erg [19-440 keV, comoving], more than 1
order of magnitude brighter than 050509b
(Bloom et al. astro-ph/0505480)."

Figures and imaging can be found at this following site:
    http://www.graasp.org/Data/050724