GRB 221009A: LCOGT Optical Afterglow Detection

We observed the GRB 221009A/Swift J1913.1+1946 (Dichiara et al., GCN 32632) field with the LCOGT 1-meter Sinistro instrument at the Teide Observatory, on Tenerife, on October 10, from 19:33 to 19:50 (corresponding to 29.38 to 29.66 hours from the GRB trigger time) with the SDSS g, r and i filters. We performed a series of 3x100s exposures in each band. We clearly detect the optical transient at the UVOT coordinates (Dichiara et al., GCN 32632), in r and i bands, and marginally in g-band (2-sigma detection), consistent with other optical detections. The following magnitudes are calculated using the Pan-STARRS catalog as reference: g = 20.87 +/- 0.36 r = 18.80 +/- 0.21 i = 17.77 +/- 0.20 These magnitudes are not corrected for galactic extinction. Further observations are planned.