TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1599 SUBJECT: GRB 021004, spectroscopic observations DATE: 02/10/07 20:50:05 GMT FROM: Peter Garnavich at U of Notre Dame F. Javier Castander (IEEC-Barcelona/U. de Chile), E. Gawiser (Yale/U. de Chile), C. Foltz, S. West (MMTO), G. Williams (MMTO/SAO), E. Falco (FLWO), T. Matheson, K.Z. Stanek (CfA), P. Garnavich (Notre Dame) and L. Macri (NOAO) report: Spectra of the GRB 021004 afterglow were obtained with the Magellan 6.5m Baade Telescope on Oct. 5.0 UT and with the MMT on Oct. 5.1, 5.3 and 6.3 UT. The spectra confirm two major MgII absorption systems at z=1.38 and z=1.60 (GCN 1569, 1579, 1582). The moderate resolution Magellan spectra show that the strong, unidentified line at 515 nm is made of 3 components separated by 0.9 nm. The MMT spectra extended to 330 nm and show no Lyman forest break implying a limit to the redshift of z<1.7. The CIV absorption in the z=1.60 system is very strong with an equivalent width of 0.5 nm (rest frame). There is another strong line 2000 km/s to the blue of the CIV which may be a second CIV component. In addition, an emission line is detected at 405.2 nm forming a P-Cygni profile with the CIV absorption. We conclude that the host is a starburst galaxy. This message may be cited.