A. Smette (NASA/GSFC,NOAO,FNRS), A. Fruchter (STScI), T. Gull (NASA/GSFC),
K. Sahu, H. Ferguson, L. Petro (STScI), and D. Lindler (ACC) report for
the HST GRB collaboration and the Danish discovery team:
The proposed optical counterpart of GRB 000301C (Fynbo et al GCN 570,
Bernabei et al. GCN 571) was observed with HST/STIS-PRISM mode during
four orbits totaling 8000s from 6.26 to 6.49 March 2000 (UT). The
MAMA NUV detector with sensitivity from 1175A to 3400A was used. Data
reductions were performed with STIS GTO IDL tools using prelaunch
spectral dispersion constants and on-orbit sensitivity calibrations.
A spectrum is detected with a peak S/N ~ 10 beginning at ~2650A,
extending to ~3250A with an average flux of ~4.6+/-0.2E-18 ergs/cm2/sec.
The emission is 2.2 pixels FWHM (0.055 arcseconds) along the slit
indicating a point source with no obvious diffuse extension. The
spectrum appears relatively flat (in f_lambda) from 3200A to 2750A and
then presents a sharp drop at about 2700A.
Within the present calibration uncertainties, the observed spectrum is
well fitted by a model using the power-law spectral index determined
by Halpern et al. (GCN 585), the observed V = 21.9 magnitude from the
STIS CCD images obtained on 6.2 March (Fruchter et al. GCN 602) a
moderate amount of extinction in the restframe of the OT, and a Lyman
limit break at ~2700A.
Assuming the Lyman break is caused by neutral hydrogen in the host
galaxy, the redshift of GRB 000301C is 1.95 +/- 0.1 where the large
error bar is due almost entirely to the present uncertainty in the
STIS UV prism calibration. We expect a more accurate calibration
We encourage ground-based observations at a predicted Lyman alpha
wavelength of 3585+-120A. H alpha would be at ~1.95 microns.
The spectrum is available at http://www.stsci.edu/~fruchter/GRB/000301C
[GCNOPS NOTE (09 Mar 00 23:50 UT): The last line of this circular
listing the URL for the spectrum as was added.]