TITLE: GCN CIRCULAR NUMBER: 27215 SUBJECT: GRB 200224B: DDOTI/OAN optical observations report DATE: 20/02/26 00:30:12 GMT FROM: Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada Margarita Pereyra (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM), Eleonora Troja (GSFC/UMD), Simone Dichiara (GSFC/UMD), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Diego Gonzalez (UNAM), Alexander Kutyrev (GSFC/UMD), and Tanner Wolfram (ASU), report: We observed the field of GRB 200224B detected by the Fermi Gamma-ray Burst Monitor (GCN 27174, Fermi trigger 604213554), with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir ( http://ddoti.astroscu.unam.mx) from 2020-02-24 06:47 to 2020-02-24 12:16 UTC (1.68 to 7.16 hours after the event). We observed a region of 13.6 degrees in RA by 20.4 degrees in declination, with a 2 x 2 grid, centered on the Fermi GBM Final Position +11:51:36 -28:52:11 J2000. This region contains about 277 square degrees. We obtained 2040 to 2520 seconds exposure across the region. We calibrated our images against the APASS catalog. Our 10-sigma limiting magnitude is around w = 19.45. Comparing to the USNO-B1, DSS DR2 and Pan-STARRS DR1 catalogs, we do not detect any uncataloged source with significant fading within the 90% probability radius of 6.3 degrees. 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