[vsnet-grb-info 2205] GRB050922C: UVES/VLT high resolution spectroscopy

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4044
SUBJECT: GRB050922C: UVES/VLT high resolution spectroscopy 
DATE:    05/09/28 16:55:22 GMT
FROM:    Silvia Piranomonte at OAR  <piranomonte at mporzio.astro.it>

V. D'Elia, S. Piranomonte, F. Fiore (INAF-OAR), S. Covino (INAF/OABr), 
L.A. Antonelli, G.L. Israel,
L. Stella, L. Sbordone (INAF-OAR), D. Fugazza,  G. Tagliaferri 
(INAF/OABr), D. Malesani (SISSA), G. Chincarini (Univ. Milano-Bicocca),
on behalf of the MISTICI collaboration, report:

"Starting on September 22, 2005 23:28:59 UT (~3.5 hours after the GRB
trigger) we have obtained high resolution spectra (R~40,000, 7.5 km/s
in the observer frame) of the optical afterglow of GRB050922C (Krimm et
al., GCN 4020, Rykoff et al. GCN 4011) using UVES at VLT/Kueyen.  The
observations consisted of 2 exposures for a total of 6000 seconds net
integration covering the full spectral range 3100-10000 Angstrom, under 
good seeing conditions. At the time of the observations the afterglow
magnitude was R~19-19.5. The resulting continuum signal to noise per
resolution element spans from 10 to 20 in the 4000-7000 Angstrom
range. The afterglow is clearly detected down to ~3300 Angstrom.
A preliminary analysis of the data shows a very rich spectrum.  We
find four main systems at z=2.199, 2.077, 2.008 and 1.9985 (the first
2 systems have been previously reported by Jakobsson et al., GCN
4029, and by Piranomonte et al., GCN 4032). The latter two systems are
shifted by only 950 km/s (rest frame). The strongest absorption lines
of the four systems are the following.

z=2.199: Lyalpha, Lybeta, OVI1032,1038, SiII1190,1193, SiII1260,
FeII1260, SiII*1264, SiII*1266, OI1302, SiII1304, OI*1304, OI*1306,
SiII*1309, CII1334, CII*1335, SiIV1393,1402, SiII*1533, CIV1548,1550,
FeII1608, FeII*1621, AlII1670, AlIII1862,1854,
FeII2344,2374,2382,2586,2600, MgII2796,2803

z=2.077: Lyalpha, OI_1302, SiII1304, CII1334, SiIV1393,1402,
CIV1548,1550, FeII1608, AlII1670, AlIII1854,
FeII2344,2374,2382,2586,2600

z=2.008 Lyalpha, CIV1548,1550, SiIV1402,1393

z=1.9885 Lyalpha, CIV1548,1550, SiIV1402,1393

Therefore,  fine-structure lines of CII*, SiII*, OI*, FeII*, witnessing
a high density environment, are detected only for the highest redshift
systems, likely associated with the GRB host galaxy.

A full analysis is underway.

We thank Paul Vreeswijk and Poshak Gandhi of the ESO staff for the 
excellent support in performing these observations in  service mode."

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