[vsnet-grb-info 1906] GRB050730: FORS1 and UVES/VLT low- and high-resolution spectroscopy

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3746
SUBJECT: GRB050730: FORS1 and UVES/VLT low- and high-resolution spectroscopy
DATE:    05/08/03 16:33:49 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <covino at merate.mi.astro.it>

V. D'Elia, A. Melandri, F. Fiore, L. Stella, L. Sbordone (INAF-OAR), G.
Tagliaferri, S. Covino, D. Fugazza, D. Malesani (INAF/OABr), G.
Chincarini (Univ. Milano-Bicocca), M. Della Valle (INAF/Arcetri), L.
Pellizza (CEA, Saclay), R. Scarpa (ESO-Chile) on behalf of the MISTICI
collaboration, report:

Starting on July 31, 2005 00:01:02 UT (about 4 hours after the GRB
trigger) we have obtained low- and high-resolution spectra (FORS1, Grism
300V, R~800; UVES, R~40,000, 7.5 km/s in the observer frame) of the
optical afterglow of GRB050730 (Holland et al., GCN 3704). The
observations consisted of 2 exposures for a total of 1800 second with
FORS1 and 2 exposures for a total of 6000 seconds with UVES covering the
full spectral range 3500-9800 Angstrom. 

At the time of the observations the afterglow magnitude was R~17.7 and
the decay of the afterglow, as measured from the FORS1 flux-calibrated
spectra, is consistent with a temporal decay index of about -1. For the
UVES spectra, the resulting continuum signal to noise per resolution
element spans from 10 to 20 in the 6000-9000 Angstrom range.

A preliminary analysis of the data confirms a very rich spectrum and all
features reported by the GRAASP collaboration (GCN 3709 and 3732). We
also detect strong, saturated, SiIV1393,1402, CIV1548,1550, CII1334,
CII*1335, Al1670, AlII1854 absorption lines at z=3.968. The main
absorption systems span a velocity range of up to 100 km/s.

A full analysis is underway.

We thank the ESO staff for the excellent support in performing these
observations in  service mode.

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