[vsnet-grb-info 8585] GRB 091024: Keck/LRIS Spectroscopy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10093
SUBJECT: GRB 091024: Keck/LRIS Spectroscopy
DATE:    09/10/27 19:12:10 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (UC Berkeley), M. M. Kasliwal and S. R. Kulkarni (Caltech)
report on behalf of a larger collaboration:

We have obtained optical spectra of the afterglow of GRB091024 (Marshall
et al., GCN 10062) with the Low Resolution Imaging Spectrometer mounted on
the 10-m Keck I telescope.  Observations began at 11:01 UT on 24 October
2009 (~ 2.1 hours after the burst) and covered the wavelength range from ~
3500 - 10000 A.

In addition to the features identified by Cucchiara, Fox, and Tanvir (CaII
H & K, Mg I), we also find strong absorption features we identify as Mg
II (2796 / 2803) and Fe II (2344, 2374, 2382, 2586, and 2600) at a common
redshift of z = 1.091.  The lack of Lyman-alpha absorption places an upper
limit of z <~ 1.9 on the redshift of GRB091024.