GRB 060502B: A Bright Early-type Galaxy as Putative Host of the Short
J. S. Bloom, D. Perley, D. Kocevski, N. Butler (UC Berkeley), J. X.
Prochaska (UCO/Lick), and H.-W. Chen report:
On 31 May 2006 UT, using Keck I (+LRIS), we obtained spectra of a
bright red extended source ("G*"; RA, DEC J2000 = 18:35:45.7,
+52:37:37) that is 11.2 arcsec South of the southern edge of the
revised XRT error circle (Troja et al. GCN 5093). Strong absorption
features, which we identify as Ca II H+K, indicate a redshift for
this early type galaxy of z=0.287. Weak [OII] emission can be seen
indicating some low level of active star formation.
We advance the hypothesis that this galaxy is the host of short burst
GRB 060502B (Troja et al. GCN 5055) based on several points:
1. The galaxy is a massive early-type similar to the putative
hosts of 050509B  and 050724 .
2. The redshift inferred of the hosts of 050509b (z=0.225) and
050724 (z=0.258) are remarkably similar to that of G* indicating
comparable energetics of the respective bursts.
3. At the redshift of z=0.287, the burst location would be
between 47 - 67 kpc in projection from the center of the putative
host, similar to the offset (39 +/- 13 kpc) inferred for 050509b.
There are viable progenitors scenarios (e.g. degenerate binary
mergers) where bursts occur at such distances from their birthsite.
4. Weak X-ray afterglow and no detected optical afterglow would
seem to indicate a low density circumburst environment, as would be
expected if the GRB originated far from the progenitor birthsite.
We recognize the difficulty of now confirming this hypothesis but
note that in the striking similarity of the host, redshift,
afterglow, and offset configuration to GRB 050509b, these
observations and inferences have a priori precedent."
A false color image will be posted at:
This message may be cited.
 Bloom et al. 2006ApJ...638..354B (astro-ph/0505480); Gehrels et
al. 2005Natur.437..851G (astro-ph/0505630)
 Berger et al. Nature 438 (2005) 988-990 (astro-ph/0508115)