[vsnet-grb-info 1969] GRB 050813: Gemini Spectra Revisited

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3808
SUBJECT: GRB 050813: Gemini Spectra Revisited
DATE:    05/08/15 07:11:14 GMT
FROM:    Josh Bloom at Harvard/CFA  <jbloom at cfa.harvard.edu>

GRB 050813: Gemini Spectra Revisited

R. J. Foley, J. S. Bloom (University of California, Berkeley), and H.-W.
Chen (MIT) report:

"We have performed an independent reduction and analysis of the spectra of
galaxies B and C in the XRT error circle of GRB 050813 (GCN 3788), and a
as yet unnamed galaxy to the north-east (referred to as X below) obtained
on Aug 14.35 UT with GMOS on Gemini-North under program GN-2005B-Q-6 and
originally reported in GCN 3801 by Berger.  Inspection of the spectrum of
galaxy X shows it to be at redshift z = 0.722 (consistent with the
redshift listed in GCN 3801 for galaxies B and C) with obvious Ca H&K and
G-band absorption but no signs of H gamma or H beta absorption.
Inspection of the spectrum of galaxy B shows it to be at redshift z =
0.718 with obvious Ca H&K absorption, but again, no signs of H gamma or H
beta absorption. Inspection of the spectrum of galaxy C shows it to not
definitively be at z = 0.722.  Although there are broad dips in the
spectrum which may correspond to Ca H&K at z = 0.722, there are other
features which conflict with this conclusion.  There are narrow emission
lines at 7353 and 7519 A observed (which would be 4270 and 4367 A at z =
0.722).

The Ca H&K lines of galaxy X have a velocity width of 591 +/- 97 km/s.
The presence of G-band absorption and a lack of emission lines points
towards an old stellar population.  The Ca H&K lines of galaxy B have a
width of 340 +/- 93 km/s.  There is also a strong (EW_observed = -6.0 A)
unidentified absorption line at 7402 A.  If we place this line at the
redshift of the galaxy, we notice that this could be Ti I 4305.  There is
an offset of 116 km/s between the line and the fiducial redshift if this
is the correct identification.  Another possibility is this line is due to
Mg II 4481 at z = 0.65."

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