TITLE: GCN CIRCULAR NUMBER: 31221 SUBJECT: GRB 211211A: NOT optical spectroscopy DATE: 21/12/12 16:24:56 GMT FROM: Daniele B Malesani at Radboud U D. B. Malesani (Univ. Radboud and DAWN/NBI), J. P. U. Fynbo (DAWN/NBI), A. de Ugarte Postigo (Obs. Cote d'Azur), L. Izzo (DARK/NBI), S. Fu, D. Xu, Z. Zhu (NAOC/CAS), N. R. Tanvir (Univ. Leicester), A. A. Djupvik (NOT), report on behalf of a larger collaboration: We observed the optical afterglow of GRB 211211A (D'Ai et al., GCN 31202; Zheng & Filippenko, GCN 31203) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Images were secured in the SDSS r, g and i filters. At the mean time of Dec 12.24 UT (16.6 hr after the GRB), we measure a magnitude r = 20.89 +- 0.05 AB, calibrated against nearby stars from the Pan-STARRS survey. Our measurement is in agreement with those by Strausbaugh & Cucchiara (GCN 31214) and de Ugarte Postigo et al. (GCN 31218), taken at a comparable epoch. Compared to the magnitudes reported by Zheng & Filippenko (GCN 31203), Ito et al. (GCN 31217) and Jang (GCN 31213), our data confirm the unusually slow decay, We report for the afterglow the following coordinates (0.3" uncertainty): RA = 14:09:10.12 Dec = +27:53:18.1 A bright, extended object (r ~ 19.5) is visible about 5.5" to the N-E of the afterglow (as already pointed out by Zheng & Filippenko, GCN 31203), which is also visible in the SDSS, Pan-STARRS, and Legacy surveys. A spectrum was secured covering both the afterglow and the nearby galaxy (wavelength range 3700-9400 AA). A weak emission line is detected on top of the host galaxy trace at 7063 AA, which could be due to Halpha at z = 0.076. This is marginally consistent with the SDSS photometric redshift 0.140 +- 0.0375, unlike other interpretations of the same line. No clear absorption or emission features are detected in the afterglow trace. This may be due to the modest S/N, and is also consistent with a low redshift, as is the detection of the afterglow in all the UVOT UV filters (Swift observation ID 1088940000). It is not clear at the present stage whether the afterglow is physically associated with the galaxy at z = 0.076. While the sky proximity and the low redshift are indeed suggestive, the physical offset at z = 0.076 would be about 8 kpc (in projection), an unusually large value for long GRBs. There is also no visible emission in the archival images down to r ~ 24 (AB) at the location of the afterglow, which would be unusual for a long GRB at z = 0.076. Moreover, if placed at z = 0.076, GRB 211211A would be an outlier of the the Amati relation (e.g. Nava et al. 2012, MNRAS, 421, 1256), with E_iso = 1.4*10^54 erg and E_peak ~ 700 keV (using the Fermi/GBM prompt properties from Mangan et al., GCN 31210). Overall, a moderate-redshift GRB (with z > 0.076) is consistent with the available information. The detection of an emerging supernova could clarify the situation. We encourage further photometric and spectroscopic follow-up of this potentially interesting event.