TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1579
SUBJECT: GRB021004: Optical Spectroscopy
DATE:    02/10/05 14:34:00 GMT
FROM:    Mike Eracleous at PSU, Astro.Dept.  <mce@astro.psu.edu>

Mike Eracleous (Penn State), Bradley E. Schaefer (U. Texas), Jeff Mader
(McDonald Obs.), and Craig Wheeler (U. Texas) report on behalf of the
Hobby-Eberly Telescope GRB followup team:

"We have obtained spectra of the optical counterpart of GRB021004 (GCN
1564) with the 9.2-m Hobby-Eberly telescope.  The observations
consisted of a series of three 15-minute exposures starting at
2002-Oct-5 3:34UT and a series of three 15-minute exposures starting
at 2002-Oct-5 8:24UT with the Marcario Low-Resolution Spectrograph.
The spectra cover the range 4200 - 9200 Angstrom at a spectral
resolution of approximately 15 Angstrom.  We detect the Mg II
absorption lines reported by Fox et al.  (GCN 1569) and confirm the
presence of two absorption systems at z=1.38 and z=1.60.  We do not
detect any significant absorption corresponding to the Mg I line at a
rest wavelength of 2853 Angstrom (with z=1.60) as reported by Fox et
al.  (GCN 1569).  We do not find any lines suggestive of absorption
systems at higher redshifts.  We also detect the Fe II UV1, UV2, and
UV3 absorption multiplets associated with both redshift systems (the
Fe II lines associated with the z=1.60 have already been reported by
Fox et al.).  In addition we also find four prominent absorption lines
at observed wavelengths of 4633, 4664, 5109, and 5152 Angstrom, which
we have not yet been able to identify.  The ratio of wavelengths
between these pair of lines approximately equals (1+1.38)/(1+1.60),
which suggests that these lines are from the same features with rest
wavelengths of 1947 and 1960 Angstroms.  The continuum shape can be
described by a power law of the form f_nu ~ nu^{-p}.  After correcting
for Galactic extinction we tentatively estimate a power-law index of 
p ~ 1.5."

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