TITLE: GCN CIRCULAR NUMBER: 13928 SUBJECT: GRB 121024A: SMARTS optical/IR afterglow observations DATE: 12/10/29 21:00:20 GMT FROM: Bethany Cobb at GWU B. E. Cobb (GWU), reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 121024A (GCN 13886, Pagani et al.) over several epochs (with mid-exposure times of 2012-10-24 03:51 UT, 06:10 UT, 08:12 UT and 2012-10-25 06:53 UT). For each epoch, several dithered images were obtained with total summed exposure times of 15 min in V and I and 12 min in J and K. For the final epoch, total exposure times were 36 min in I and 30 min in J. The fading afterglow of GRB 121024A (e.g. GCN 13887, Klotz et al.; GCN 13888, Jelinek et al.; GCN 13891, Knust et al.) was detected with the following magnitudes (or 3-sigma limits): mid-exposure time (hours) I mag J mag K mag 0.90722 18.0 +/- 0.1 16.7 +/- 0.1 15.2 +/- 0.2 3.23611 19.4 +/- 0.1 17.9 +/- 0.1 16.3 +/- 0.2 5.27333 19.8 +/- 0.1 > 18.0 > 16.4 27.95278 > 21.9 > 19.3 ... (Optical photometry is calibrated against USNO-B1.0 stars and IR photometry is calibrated against 2MASS stars in the field.)