TITLE: GCN CIRCULAR NUMBER: 26977 SUBJECT: GRB 200131A: Further RATIR Optical Observations DATE: 20/02/03 19:22:08 GMT FROM: Nat Butler at Az State U Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report: We observed the field of GRB 200131A (Sbarufatti et al., GCN 26953) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2020/02 2.10 to 2020/02 2.17 UTC (27.70 to 29.45 hours after the BAT trigger), obtaining a total of 1.42 hours exposure in the r and i bands, and from 2020/02 3.10 to 2020/02 3.12 UTC (51.69 to 52.28 hours after the BAT trigger), obtaining a total of 0.49 hours exposure in the r and i bands. The optical transient (Lipunov et al., GCN Circ. 26954, Butler et al., GCN Circ. 26957, Strausbaugh et al., GCN Circ. 26959, Gokuldass et al., GCN Circ. 26960, Pozanenko et al., GCN Circ. 26964 & 26965) is detected on 2020/02/02 with: r = 21.39 +/- 0.11 i = 21.39 +/- 0.07 and on 2020/02/03 with: r = 22.26 +/- 0.29 i = 22.45 +/- 0.35 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.