TITLE: GCN CIRCULAR NUMBER: 18072 SUBJECT: GRB 150724B: RATIR Optical Observations DATE: 15/07/27 03:33:50 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We observed the field of the LAT GRB 150724B (Bissaldi et al., GCN 18065) 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 2015/07 26.28 to 2015/07 26.48 UTC (36.02 to 40.86 hours after the BAT trigger), obtaining a total of 2.39 hours exposure in the r and i bands. For a source within the Swift XRT error circle (Osborne et al., GCN 18069), in comparison with the SDSS DR9 catalog, we obtain the following detections: r 23.24 +/- 0.34 i 22.39 +/- 0.15 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. At this moment we have no information on fading. Further observations are planned. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.