TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4356 SUBJECT: GRB051211A: possible optical candidate DATE: 05/12/15 14:13:31 GMT FROM: Cristiano Guidorzi at ARI,Liverpool JMU C. Guidorzi, A. Monfardini, I.A. Steele, A. Gomboc, C.G. Mundell, C.J. Mottram, R.J. Smith, D. Bersier, A. Melandri, S. Kobayashi, D. Carter, M.F. Bode (Liverpool JMU), N. Tanvir (Hertfordshire) report: "The 2-m Faulkes Telescope North observed GRB051211A discovered by HETE-2 (Atteia et al, GCN 4324) from 5.9 to 11.9 hours after the burst. So far, searches for afterglow have provided just upper limits in the optical (de Ugarte Postigo et al. GCN 4325 & GCN 4335, Klotz et al. GCN 4329, Jelinek et al. GCN 4333, Maeno et al. GCN 4339, Blustin et al. GCN 4342, Zhuchkov et al. GCN 4344) as well as in the X-rays (Cusumano et al. GCN 4326). From the comparison of two 30-min stacked images, we found an object at RA=06:56:09.0, DEC= +32:40:06.4 (J2000) showing some evidence of a fading of 0.6 +- 0.3 mag (calibrated with USNOB stars of the field, with an uncertainty of 0.4 mag affecting just the absolute values, but not the relative ones). It lies 63 arcsec away from the HETE-2 centroid (given with an error radius of 80 arcsec at 90% CL). ----------------------------------------------------- Start Time Filter Exposure Mag since GRB 6.3 hr R 12x150s 21.15 +- 0.15 11.4 hr R 12x150s 21.75 +- 0.20 ----------------------------------------------------- This candidate does not match any DSS source, although we notice a small blur in the DSS IR that might be either a faint source or a background fluctuation. If we assume the fading is genuine, the average temporal decay power-law index turns out to be around 1.0 +- 0.5. However, a word of caution is required, as the source magnitude is close to the limiting value affected by the moonlight. An image of the OT candidate at both epochs is available at the following: http://www.astro.livjm.ac.uk/~crg/GRB051211A_possible_OT_FTN.jpg We encourage further observations."