TITLE: GCN CIRCULAR NUMBER: 14374 SUBJECT: GRB 130408A: SMARTS optical/IR afterglow observations DATE: 13/04/12 20:46:37 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 130408A (GCN 14361, Lien et al.) over several epochs (with mid-exposure times of 2013-04-09 00:30 UT, 02:15 UT, 03:41 UT and 2013-04-11 02:24 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 130408A (e.g. GCN 14362, Melandri et al.; GCN 14363, Siegel et al.; GCN 14364, Sudilovsky et al.) was detected with the following magnitudes (or 3-sigma limits): mid-exposure time (hours) I mag J mag K mag 2.64611 18.8 +/- 0.1 17.8 +/- 0.1 > 16.1 4.38444 19.6 +/- 0.1 18.6 +/- 0.2 16.8 +/- 0.2 5.82472 20.0 +/- 0.1 18.6 +/- 0.2 > 17.2 52.53694 > 21.5 > 19.6 ... (Optical photometry is calibrated against USNO-B1.0 stars and IR photometry is calibrated against 2MASS stars in the field.) Between about 2.6 hrs and 5.8 hrs post-burst, the GRB afterglow fades with a decay rate of approximately alpha = 1.4 (where afterglow flux is proportional to t^-alpha).