GCN Circular 15058
Martin Topinka, Lorraine Hanlon, Martin Jelinek and Seamus Meehan, on behalf of the Watcher telescope team, report: We followed the Swift detection of GRB 130727A (Stroh et al., GCN Circ. 15046, Swift trigger 564342) with the Watcher robotic telescope (D=40cm) located at Boyden Observatory, near Bloemfontein in South Africa. We started imaging the field at 16:59:43 UT on 2013-07-27 (14m 23s after the BAT trigger, 25s after receiving the GCN trigger) taking 60s exposures in the clear filter (C) using an Andor CCD camera. No optical counterpart is detected within the XRT/UVOT error circle (Goad et al./De Pasquale et al., GCN Circ. 15051/15056) in any of the individual 60s images either in a combined image covering time from 17:01:55 UT to 17:11:40 UT with the total exposure of 540s. Image analysis yields the limiting magnitude of ~18.9 +/- 0.1. Start | End | Exposure | Filter | Limiting mag. | Limiting mag. error 17:01:55 UT | 17:11:40 UT | 540s | C | > 18.9 | 0.1 This message is quotable in publications.