TITLE: GCN CIRCULAR NUMBER: 22042 SUBJECT: GRB 171020A: Continued RATIR Optical and NIR Observation DATE: 17/10/22 21:19:00 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), 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 171020A (Page, et al., GCN 22028) 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 2017/10 22.13 to 2017/10 22.47 UTC (27.94 to 36.23 hours after the BAT trigger), obtaining a total of 5.27 hours exposure in the r and i bands and 2.21 hours exposure in the Z and Y bands. We contine to detect the optical transient (Malesani, et al., GCN 22029; also, Moskvitin, et al., GCN 22031; Butler, et al., GCN 22037). In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limits (3-sigma): r = 23.25 +/- 0.14 i = 23.01 +/- 0.11 Z > 21.75 Y > 22.05 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Compared to our observations last night, these data suggest either a slow afterglow fade (~t^-0.2) or that our measured flux contains flux from the GRB host galaxy. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.