TITLE: GCN CIRCULAR NUMBER: 13765 SUBJECT: GRB 120913B: TAROT La Silla observatory optical detection DATE: 12/09/14 00:41:33 GMT FROM: Alain Klotz at CESR-CNRS Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR), Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report: We imaged the field of GRB 120913B detected by SWIFT (trigger 533613) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 30.6s after the GRB trigger (17.7s after the notice). The elevation of the field decreased from 26 degrees above horizon and weather conditions were good. We detect a new fading source in the error box given by SWIFT. We detected the candidate couterpart mentioned by LaCluyze et al. (GCNC 13764) at the following position (+/- 2 arcsec): RA(J2000.0) = 14h 14m 38.57s DEC(J2000.0) -14d 30' 55.8" OT raised until R=15.8 5 min after the GRB. Now the afterglow is fading. Magnitudes were estimated with the nearby NOMAD1 star 0754-0289300 (R.A.=213.6332611 Decl=-14.5238889 J2000) R=15.99. MAgnitutes are not corrected for galactic dust extinction. N.B. Galactic coordinates are lon=331.3041 lat=+43.7095 and the galactic extinction in R band is about 0.2 magnitude estimated from D. Schlegel et al. 1998ApJ...500..525S. This message may be cited.