TITLE: GCN CIRCULAR NUMBER: 10443 SUBJECT: GRB 100219A - Gemini South Spectroscopy DATE: 10/02/20 06:58:52 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko, J. S. Bloom, D. A. Perley, and B. E. Cobb (UC Berkeley) report on behalf of a larger collaboration: We have obtained spectra of the proposed host galaxy (Bloom and Nugent, GCN 10433; Holland et al., GCN 10436) and the optical afterglow (Jakobsson et al., GCN 10438; Kruehler et al., GCN 10439) of GRB100219A (Rowlinson et al., GCN 10430) with the Gemini Multi-Object Spectrograph mounted on the 8-m Gemini South telescope. Our first sequence of 2 x 900 s observations started at 2:44 UT on 20 February 2010 and cover the range from 6500 - 9500 A. Only the proposed host galaxy was contained on the slit for these spectra. Our second set, starting immediately afterward, cover the wavelength range from 4500 - 7500 A and both the proposed host and afterglow are positioned on the slit. From the nearby galaxy, we detect strong emissions features corresponding to H-alpha, H-beta, and [O III] at a common redshift of z = 0.217. The spectrum of the afterglow shows a strong break at ~ 6880 A, with only faint continuum blueward of this feature. Interpreting this as the Lyman-alpha break, this correponds to a redshift of z ~ 4.7. We find marginal evidence for narrow absorption features corresponding to Si II and Si II* at z = 4.65 redward of the break - however the relatively low signal-to-noise ratio of our spectrum in this regime makes this result somewhat uncertain. Our derived redshifts for both objects are similar to, though slightly less than, the values derived by Groot et al. (GCN 10441) from the VLT/X-shooter. They are also consistent with the photometric redshift of z ~ 4.5 derived by Kruehler et al. (GCN 10439) from GROND.