TITLE:   GCN CIRCULAR
NUMBER:  5715
SUBJECT: GRB 061007: Magellan Spectroscopy
DATE:    06/10/08 07:51:33 GMT
FROM:    Hsiao-Wen Chen at U Chicago  <hchen@oddjob.uchicago.edu>

David Osip (Las Campanas Observatory), H.-W. Chen (U Chicago), and J. X. Prochaska (UCO/Lick Observatory) report on behalf of a larger collaboration:

"We observed the afterglow of GRB061007 reported by Rykoff & Rujopakarn (GCN 
5706) and confirmed by Mundel et al. (GCN5708) and Bersier et al., using the 
LDSS3 with a 0.75-arcsec slit on the Magellan Clay telescope at the Las
Campanas Observatory.  The observations started at 03:54:00 UT on October 8, 
2006, ~ 18 hours after the inital Swift/BAT trigger, and were carried out 
under a mean seeing condition of 0.75 arcsec in a sequence of five 1200-sec 
exposures.  The final stacked spectrum covers the spectral range from 3900 
Ang to 6500 Ang with a spectral resolution element of 2.4 Ang.  In the 
spectrum, we identify a strong MgII absorption system, accompanied with 
FeII 2344 and 2600 transitions) at z=1.261.  We consider this the likely 
redshift of GRB061007, given the absence of a strong Lya feature (or any 
other strong metal-line transitions) in our spectrum.  We also report an 
intervening MgII system at z=1.06.

Further analysis is underway.

This message may be cited."