TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3716
SUBJECT: GRB 050730, spectra and optical photometry
DATE:    05/07/31 06:44:05 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

M. Holman (CfA), P. Garnavich (Notre Dame), K.Z. Stanek (Ohio State)

Spectra of the afterglow of GRB 050730 (Holland et al. GCN 3704)
were obtained with the Magellan Observatory Baade Telescope and
IMACS imaging spectrograph beginning 2005 July 30 23:57 (UT).
The spectra cover 360 to 950 nm with a dispersion of 0.74 A/pix.
We find a clear Ly-alpha absorption system with the GRB flux
reaching zero between 598 nm and 609 nm.  This confirms the
redshift of 3.97 found for the burst by Chen et al.
(GCN 3709) and Rol et al. (GCN 3710).

An image of the GRB field was obtained July 30 23:10 (UT) with
IMACS and the afterglow flux calibrated with Landolt standard
SA110-360. We estimate the afterglow brightness at R=17.50+/-0.05
mag. A star to the west of the afterglow at
14:08:14.62 -03:46:29 (2000) has a brightness of R=17.18+/-0.05 mag.

A plot of the spectrum and the image of the afterglow obtained with
IMACS are available at http://www.nd.edu/~pgarnavi/grb050730 .