TITLE: GCN CIRCULAR NUMBER: 26911 SUBJECT: GRB 200125B: DDOTI/OAN optical observations report DATE: 20/01/28 06:04:23 GMT FROM: Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada Margarita Pereyra (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM), Eleonora Troja (GSFC/UMD), Diego Gonzalez (UNAM), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Tanner Wolfram (ASU), Simone Dichiara (GSFC/UMD) report: We observed the field of GRB 200125B detected by Fermi Gamma-ray Burst Monitor (Fermi GBM Team, GCN Circ. 26879, Veres et al., GCN Circ. 26893), with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) from 2020-01-26 02:18 to 2020-01-26 06:53 UTC (5.58 to 10.16 hours after the event). We observed a region of 6.8 degrees in RA by 10.2 degrees in declination centered on the GBM Final Position 00:29:47 +64:41:22 J2000. This region contains about 70 square degrees. We obtained about 3.1 hrs total exposure across the region. We calibrated our images against the APASS catalog. Our 10-sigma limiting magnitude is w = 20.04 for a 2.0 degrees radius error region centered at the GBM Final Position. Comparing to the USNO-B1 and PAN-STARRS DR1 catalogs we do not detect any uncataloged source with significant fading or rising to our 10-sigma limit. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. -- *Dr. Margarita Pereyra * *FFTF, Schlumberger Foundation Alumnae* ---------------------------------------------------------------------------------------------------------------- *Catedrático Conacyt* *Instituto de Astronomía de la UNAM,* *Km. 107 Carretera Tijua**na-Ensenada, * *Ensenada Baja California, México. C.P. 22860* Oficina: 405 Skype: margarita-pereyra