TITLE: GCN CIRCULAR NUMBER: 29273 SUBJECT: GRB 210104A: SARA-KP 0.9m Optical Afterglow Detection DATE: 21/01/06 22:01:36 GMT FROM: Samalka Anandagoda at Clemson University S. Anandagoda, S. Geier, K. Pellegrin and D. Hartmann report: We observed the field of GRB 20210104A (Fermi GBM Team, GCN 29232; Troja et al., GCN 29233; Biltzinger et al., GCN 29234) using the SARA 0.9m optical telescope located at Kitt Peak, AZ, USA, equipped with the Alta-E6-1105 camera. Observation started at 06:20:04 UTC on 2021-01-05 and ended at 09:34:43 UTC (~ 18 to 21 hours after the detection of the burst by the Fermi GBM Team). We obtained a series of 120s exposure frames in the Bessell R filter. We clearly detect the optical afterglow of GRB 20210104A at the enhanced Swift-XRT position (Beardmore et al., GCN 29245). The estimated magnitude of the GRB afterglow was 20.61 found by stacking 20 images of 120s each in the Bessell R band filter. T_start-T0 (hrs) T_end-T0 (hrs) Start Date (UTC) Filter Magnitude (mag) —————————————————————————————------------------------- ---------------------------------------------------------------------------------------------------------------- 18:53 19:33 2021-01-05T06:20:04 R 20.61 Photometry is done based on the USNO-B1.0 catalog. The Southeastern Association for Research in Astronomy (SARA) consortium operates three telescopes: the 0.9-m SARA-KP at Kitt Peak in Arizona, and the 0.6-m SARA-CT at Cerro Tololo in Chile, and the 1.0-m SARA-RM (formerly the JKT) telescope at Roque de los Muchachos Observatory in the Canary Islands. For more information see: Keel et al. (2016): https://iopscience.iop.org/article/10.1088/1538-3873/129/971/015002