GCN Circular 11502
K. Wiersema, N. Tanvir (Leicester) and A. Levan (Warwick) report: We observed the afterglow of GRB 101225A (Racusin et al. GCN 11493; Xu et al. GCN 11496) with the 4.2m William Herschel Telescope. We used the ACAM instrument to obtain imaging in r and i filters, and low resolution spectroscopy. The afterglow is clearly detected in individual images of 300 second exposure, at R=22.8 +/- 0.2 mag (uncertainties are dominated by scatter in USNO-B star magnitudes), at 28.2 hrs after burst. The source appears pointlike, in the 1.1 arcsecond seeing conditions. We note that this magnitude compared with the Xu et al value (GCN 11496) implies a very shallow decay. We obtained two low resolution spectra immediately following the imaging, each with 1200 second exposure time. Continuum emission is detected in the 5000 - 9300 A range, but no significant emission or absorption lines are detected. Detection of continuum up to 5000 A gives a formal constraint on the redshift of z<3.1. At the redshift estimated by Campana et al. (GCN 11501) we would expect to detect emission lines in the ACAM spectra (e.g. Balmer lines, [O III]), implying that the spectrum is either strongly dominated by the afterglow (the host is faint) or that the emission lines are redshifted into wavelength areas dominated by strong skylines. We thank Ovidiu Vaduvescu for excellent support.