TITLE: GCN CIRCULAR NUMBER: 23253 SUBJECT: GRB 180914B: DDOTI/OAN Detection and Confirmation of Fading DATE: 18/09/18 00:55:28 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), Eleonora Troja (GSFC), Rosa L. Becerra (UNAM), William H. Lee (UNAM), and Alexander Kutyrev (GSFC) report: We observed the field of GRB 180914B (Ursi et al., GCN Circ. 23226) with the DDOTI/OAN wide-field imager at the Observatorio Astronomico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2018-09-16 02:54 to 06:02 (32.5 to 35.7 hours after burst) and 2018-09-17 02:58 to 04:17 (56.6 to 57.9 after burst) obtaining 7200 and 3060 seconds exposure with no filter. We detect the optical counterpart (Zheng & Filippenko, GCN Circ. 23237; Troja, et al., GCN Circ. 23238) with the following magnitudes: w = 19.45 +/- 0.10 (on 2018-09-16) w = 20.25 +/- 0.31 (on 2018-09-17) These AB magnitudes are calibrated against the Pan-STARRS1 catalog and are not corrected for Galactic extinction in the direction of the GRB. We confirm the fading reported by de Ugarte Postigo et al. (GCN Circ. 23239), Troja et al. (GCN Circ. 23243), and Mazaeva et al. (GCN Circ. 23249). DDOTI/OAN imaged the entire Fermi/LAT error region (Bissaldi et al., GCN Circ. 23232). We confirm that there were no other uncatalogued sources in the region on 2019-09-16 to a 10-sigma limit of w = 19.4. We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.