TITLE: GCN CIRCULAR NUMBER: 17877 SUBJECT: GRB 150527A: LCOGT McDonald observations DATE: 15/05/27 09:02:38 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy J. Japelj (U. Ljubljana), C. Guidorzi (U. Ferrara), C.G. Mundell (U. Bath), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of a larger collaboration report: The 1-m LCOGT McDonald unit began observing Swift GRB 150527A (Evans al GCN 17874) on May 27 at 06:56:33 UT (~7.6 minutes after the burst trigger) with SDSS r and i filters. Inside the Swift-XRT error circle we provide conservative limits on detection down to the following limiting magnitudes: Mid Time Exposure Filter Magnitude (s) (s) --------------------------------------------------- 795 5x120 r' > 19.5 1500 5x120 i' > 18.3 --------------------------------------------------- These values are compatible with the source reported by RATIR (Butler et al. GCN 17876), although no information about its position is reported. We note the presence of a faint source in our coadded image with i'=20.6 +- 0.4 mag at the following position: RA(J2000)=19:15:50.31, Dec(J2000)= +04:12:05.0. However, we caution that the field is crowded, Galactic dust extinction towards this field is high, A_V = 2.7 mag (Schlafly et al. 2011). Calibration is done against nearby USNOB-1 stars.