TITLE: GCN CIRCULAR NUMBER: 15989 SUBJECT: GRB140318A: Discovery Channel Telescope Optical Detection DATE: 14/03/18 06:55:48 GMT FROM: John Capone at UMD J. Capone (UMD), E. Troja (NASA-GSFC), V. Toy (UMD), S.B. Cenko (NASA-GSFC), A. Kutyrev (NASA-GSFC), A. Cucchiara (NASA-GSFC), S. Veilleux (UMD), and S. Gezari (UMD) report on behalf of a larger collaboration: We observed the field of GRB140318A (Cenko et al., GCN 15986) with the Large Monolithic Imager (LMI) on the recently commissioned 4.3m Discovery Channel Telescope (DCT) at Happy Jack, AZ. We started a sequence of r', i' and z' images beginning at 2014-03-18 03:32 UTC (approximately 3.5 hours after the Swift trigger). A source is clearly detected in all filters at the location of the optical afterglow (Schulze et al, GCN 15987). Using nearby point sources from SDSS for calibration, we measure preliminary magnitudes of r' = 21.6 +/- 0.2, i' = 21.14 +/- 0.06 and z' = 20.86 +/- 0.04 at an average time of ~5 hours after the GRB. These values are not corrected for Galactic extinction in the direction of the GRB. The source shows evidence of fading when compared with the NOT observation, confirming that this is the optical afterglow. Additional multi-band observations are ongoing. We thank the staff of the Discovery Channel Telescope for assistance with these observations.