TITLE: GCN CIRCULAR NUMBER: 17228 SUBJECT: GRB 141221A: Keck spectroscopy DATE: 14/12/25 13:26:00 GMT FROM: Daniel Perley at Caltech D. A. Perley, Y. Cao (Caltech), and S. B. Cenko (GSFC) report: We observed the optical afterglow of GRB 141221A (Sonbas et al., GCN 17206) with the DEIMOS spectrograph on the Keck II telescope between 12:48 and 13:10 UT on 2014-12-21. Two 900-second exposures were acquired at high airmass. We detect significant continuum flux across the entire spectral range between 4490-9660 Angstroms. Inspection of the 1D spectrum shows two apparent absorption features at 6854 and 6873 Angstroms which we tentatively associate with the Mg II doublet at z=1.452. Lower-significance probable absorption lines are also seen at the wavelengths of the Fe II 2599, 2585, 2383, 2374, and 2344 lines at similar redshift, lending additional credence to this association. However, due to a failure of the blue arc calibration lamps, we note that our wavelength solution is preliminary and this result should be considered tentative.