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GCN Circular 1633

GRB021004: High-resolution optical spectroscopy
2002-10-14T14:30:23Z (22 years ago)
Angelo Antonelli at Obs. Astro. di Roma <>
S. Savaglio (INAF-OAR and JHU), F. Fiore, G. Israel, G. Marconi,
L.A. Antonelli, A. Fontana, L. Stella, A. Di Paola, G. Stratta (INAF-OAR),
S. Covino, G. Chincarini, G. Ghisellini, P. Saracco, F. Zerbi (INAF-OABrera),
D. Lazzati (Cambridge, UK), R. Perna (CfA), M. Vietri (Univ. Roma Tre),
F. Frontera (Univ. di Ferrara), S. Mereghetti (CNR-IASF),
E.J.A. Meurs (Dunsink Obs.) and N. Kawai (Titech, RIKEN) report:

"Starting on October 05 2002 01:37 UT we have obtained high resolution
spectra (R=50,000, 6 km/s in the observer frame) of the optical
afterglow of GRB021004 (Fox et al., GCN #1564) using UVES at VLT.  The
observations cover the full spectral range 3200-9800 Angstrom, in good
seeing conditions. At the time of the observations the afterglow
magnitude was R~18.6 and B~19.0.

A preliminary analysis of the first hour of observation reveals
several absorption lines associated with at least 4 metal systems
(also see Salamanca et al., GCN #1611).

The z=2.321,2.327 system is probably very close to the GRB itself or
the circumburst medium. C IV absorption lines associated with this
system are in fact extremely strong and complex, spanning a velocity
range of about 1000 km/s. This system may show the so called "line
locking", possibly relativistic, effect, where the second component of
the z=2.321 C IV doublet is "locked" to the first component of the
z=2.327 C IV doublet. This effect has been observed in the past in
narrow absorption systems associated with high redshift quasars (e.g.
Wampler 1991, ApJ, 368, 40) and O stars (Lucy & Solomon, 1970, ApJ,
159, 879).

Low ionization lines of AlII1670 and possibly SiII1526 are also
detected in the red wing of the z=2.327 component. Low ionization
lines are not detected in the lower redshift system at z=2.321.

The z=2.2958,2.2985 system is shifted by ~2500 km/s blueward of the
strong z=2.321,2.327 system and shows much weaker, but still very
strong, C IV lines and no low ionization lines. The velocity range of
this absorption is of about 300 km/s.

The z=1.6019 intervening system shows a narrow Al III absorption with
column density of log N(AlIII)=13.2 +\- 0.1 and Doppler parameter b=12
+\- 1 km/s.

The other system at z=1.38 shows a complex structure with at least 4
components spanning a velocity range of about 200 km/s.  The FeII
column densities suggest that this system may be associated with a
Damped Lyman Alpha system in the interstellar medium of an intervening

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