GCN Circular 21807
A. Cucchiara, D. Morris, J. Staff, and B. Gendre (U. Virgin Islands) report on behalf of a larger collaboration: "On August 27.71 UT (T_0 +12.0h) we began observing the center of the field of GRB 170827A (Marshall et al. GCN 21718, D'Ai et al. GCN 21730) using the Las Cumbres Observatory 1m telescope located in Sutherland Observatory. We performed a series of 5x240s observations in SDSS r' and i��� bands for a total of 20 minutes on sky in each filter at average airmass of 1.05. In the full median stacked images we identified no optical counterpart within the center of the Swift-XRT refined position or at the ePESSTO NTT optical counterpart location (Evans et al. GCN 21413, Lyman et al. GCN 21728) at the following 3-sigma limits: r' > 20.6 mag i' > 19.6 mag These values are consistent with the limits and detections reported by other observatories (D'Avanzo et al. GCN 21721, Schady et al. GCN 21729, 21743). These magnitudes are calibrated against nearby USNO-B1 sources, converted in SDSS bands, and not corrected for Galactic extinction."