R. Chornock, D. A. Perley, S. B. Cenko, J. S. Bloom, B. Cobb (UC
Berkeley), and J. X. Prochaska (UCO/Lick) report:
We began a spectroscopic integration on the afterglow of GRB 090313
(Chornock et al., GCN 8979; Mao et al., GCN 8980) using Gemini-South
(GMOS) starting at 04:20 UT on 2009-03-14, approximately 19 hours after
the trigger. We conducted a series of two exposures of 600 seconds each
using the R400 grating, covering a wavelength range of approximately
3900 to 8140 Angstroms. Additional exposures are in progress.
We detect transitions corresponding to C IV, Al II, O I, Si II, Si IV,
and Fe II, as well as a broad absorption feature which we associate with
Lyman-alpha, at a common redshift of z=3.375. We also detect Si II* at
this redshift, identifying this as the redshift of the GRB. While
ruling out an association with the bright nearby SDSS galaxy, this
redshift suggests an extraordinary late-time afterglow luminosity. We
continue to encourage sustained late-time follow-up of this event, which
given its continued brightness (Perley et al., GCN 8985; de Ugarte
Postigo et al., GCN 8992) is likely to continue to be observable to
small-aperture telescopes for an extended period of time.
We thank the Gemini staff for conducting these observations.