TITLE: GCN CIRCULAR NUMBER: 23820 SUBJECT: GRB 190129B: DDOTI Detection of the Possible Afterglow and Suggestion of Fading DATE: 19/01/30 20:32:24 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Nat Butler (ASU), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Diego González (UNAM), William H. Lee (UNAM), Margarita Pereyra (UNAM), Alexander Kutyrev (GSFC), Eleonora Troja (GSFC), and Tanner Wolfram (ASU) report: We observed the entire IPN error box of GRB 190129B (Hurley et al., GCN Circ. 23808) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) from 2019-01-30 02:15 UTC to 12:48 UTC (14.0 to 24.5 hours after burst) obtaining a total of 4.4 hours exposure in the w filter. If we split our exposures roughly in two, in the first half from 02:15 to 05:40 UTC we clearly detect a faint source close to the error region for the candidate XRT afterglow (LaPorte et al., GCN Circ. 23813) at 07:49:50.82 +00:56:06.1 J2000 (+/- 0.5 arcsec). In the second half from 05:41 to 12:48 UTC, this source is not visible. The presence of a nearby bright star complicates photometry. However, in the difference image we measure a magnitude and 1-sigma error of w = 22.7 +/- 1.0. Our w magnitudes are calibrated against the USNO-B1 catalog (adjusted to an approximate AB system) and are not corrected for Galactic extinction in the direction of the GRB. We assume this source corresponds to the sources reported previously by Bolmer & Steinle (GCN Circ. 23814) and Piranomonte et al. (GCN Circ. 23818) at a similar position and magnitude. However, our observations are the first to suggest fading, albeit at low significance. We thank the DDOTI technical team and the staff of the Observatorio Astronómico Nacional.