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GCN Circular 8372

Subject
GRB 081008: Galaxy associated with z=1.967 absorber
Date
2008-10-14T00:17:32Z (16 years ago)
From
Antonino Cucchiara at PSU <cucchiara@astro.psu.edu>
A. Cucchiara, D. B. Fox (Penn State), S. B. Cenko  (Berkeley) and E. Berger
(Harvard) report on behalf of a larger collaboration:

"Analysis of the Gemini-South GMOS r-band acquisition image taken on 
October 8
(Cucchiara et al., 8346) shows the presence of an extended source at 
2-arcsec
distance from the afterglow of GRB 081008.  The source is serendipitously
located in the GMOS slit during our spectroscopic observations.

Extracting the spectrum of this object reveals the presence of metal 
absorption
features including FeII(1608), AlII(1670), NiII(1703), AlIII(1854), and
CrII(2056,2062,2066) at a common redshift z=1.967.  We conclude that this
galaxy is associated with the strong z=1.967 absorber observed in the GRB
afterglow spectrum, and is a candidate host galaxy to the GRB.

The galaxy is located at (J2000) RA 18:39:49.64, Dec -57:25:53.41.  At 
z=1.967
its 2.1-arcsec offset from the line of sight to GRB 081008 corresponds 
to 16 kpc
in projection.

We report the R-band magnitude of the GRB and the Host, calibrated using 
USNO
catalog magnitudes of 4 nearby USNO stars:  At the time of the 
acquisition image,
00:01 UT, we find R=18.32 +- 0.1 mag for the GRB afterglow, and R=20.75 
+- 0.1
mag for the galaxy.

The observed host galaxy magnitude corresponds to an absolute AB 
magnitude (at
central wavelength 220 nm in the host galaxy frame) of M_220(AB) = -21.5 
mag;
assuming a comparable rest-frame B-band luminosity would place this galaxy
among the brightest GRB host galaxies if it is the host galaxy of GRB 081008
(Berger et al., Apj 2007, 657).

While we cannot confirm a host identification at this time, we note that the
presence of an associated DLA in the VLT/FORS2 spectrum (d'Avanzo et al.,
GCN 8350), along with the reported absence of any absorption signature due
to neutral hydrogen at z>1.967, both support this suggestion."


-- 

Antonino Cucchiara
PhD candidate
Department of Astronomy&Astrophysics
Penn State University
website: www.astro.psu.edu/~cucchiara/
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