TITLE: GCN CIRCULAR NUMBER: 10648 SUBJECT: GRB 100418A: Continued PAIRITEL NIR Observations DATE: 10/04/22 12:36:14 GMT FROM: Adam Morgan at U.C. Berkeley A. N. Morgan, D. A. Perley, C. R. Klein, and J. S. Bloom (UC Berkeley) report: We continued to observe the location of the optical afterglow of GRB 100418A (Marshall et al., GCN 10612) with the 1.3m PAIRITEL located at Mt. Hopkins, Arizona for a second epoch beginning at 2010-04-20 07:59 UT, ~34.8 hours after the Swift trigger. In mosaics (effective exposure time of 1.27 hours) taken simultaneously in the J, H, and Ks filters, we observe that the afterglow has faded approximately 1 magnitude since our first epoch (Klein et al., GCN 10627). Unfortunately, poor weather conditions prevented further observations on 2010-04-21 and 2010-04-22. The preliminary photometry yields: post burst t_mid (hr) exp.(hr) filt mag m_err 35.81 1.27 J 18.0 0.1 35.81 1.27 H 17.2 0.1 35.81 1.27 Ks 16.3 0.1 All magnitudes are given in the Vega system, calibrated to 2MASS. No correction for Galactic extinction has been made to the above reported values.