GCN Circular 9008
B. E. Cobb (UC Berkeley) reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 090313 (GCN 8980, Mao et al.) over four epochs (with UT mid-exposure times of: 2009-03-14 04:27, 2009-03-14 06:55, 2009-03-15 06:30 & 2009-03-17 05:07). Total summed exposure times for each observation amounted to 36 minutes in R and 30 minutes in J. The GRB afterglow (e.g. GCN 8979, Chornock et al., GCN 8983, Updike et al. and GCN 8985, Perley et al.) appears in our imaging to be fading rapidly after ~19 hours post-burst: mid-exposure time (hours post-burst) R mag J mag 19.33 19.70+/-0.04 17.38+/-0.15 21.81 19.90+/-0.04 17.62+/-0.15 45.38 21.57+/-0.12 18.91+/-0.16 92.01 > 22.5 > 19.8 These preliminary magnitudes are calibrated using Landolt standard stars in the optical and a 2MASS star in the IR. This rapid fading follows the initial plateau phase that was reported by Perley et al. (GCN 8985) and de Ugarte Postigo et al. (GCN 8992). This fading is consistent with the light curve break noted by de Ugarte Postigo et al. (GCN 8999), though the break appears to occur in this imaging somewhat earlier than suggested by Yoshida et al. (GCN 9002).