TITLE: GCN CIRCULAR NUMBER: 11853 SUBJECT: GRB 110328A / Swift J164449.3+573451: Infrared transient DATE: 11/03/31 18:19:39 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan (U. Warwick), D. Perley (U.C. Berkeley), N.R. Tanvir (U. Leicester), J. Bloom, S.B. Cenko (U.C. Berkeley) report for a larger collaboration: "We re-observed the localization of GRB 110328A with Gemini-N/NIRI on 31 March 2011. Observations were taken in the K-band, and began at 13:15UT, roughly 24 hours after our previous observation (Levan et al. GCN 11846). We find that the IR source, coincident with the X-ray (Osborne et al. GCN 11826) and radio (Zauderer et al. GCN 11848) localisations has faded by 0.25 +/- 0.03 magnitudes over this time frame. Hence we conclude that the IR light does contain a substantial contribution from transient emission. We note that the apparent brightening of the source in a few hours between the observations of Morgan et al. (GCN 11845) and Gemini (GCN 11846), coupled with the fading over the subsequent 24 hours, suggests that the behaviour of the system is complex, and as in the X-ray, is not simply modelled by either a rising, or decaying lightcurve. The location of the source is consistent with the galaxy observed in the optical with a measured redshift z=0.351, (Levan et al. GCN 11833, Thoene et al. GCN 11834) hence increasing the confidence in a true association. Further observations are planned."