TITLE: GCN CIRCULAR NUMBER: 10727 SUBJECT: GRB 100418A: Keck imaging DATE: 10/05/07 23:19:17 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley, S. B. Cenko, A. A. Miller, D. Poznanski, A. V. Filippenko, J. S. Bloom (UC Berkeley), and P. Nugent (LBNL) report: We imaged the field of GRB 100418A (Marshall et al., GCN 10612) with the Low Resolution Imaging Spectrometer on the Keck I 10-m telescope during morning twilight on 2010-05-06 UT. Two exposures of 380 seconds each were acquired in the g and R bands simultaneously. The midpoint of the observation was 14:54 UT, 17.739 days after the GRB. At the position of the afterglow and calibrating to 9 nearby unsaturated SDSS stars, we measure magnitudes of: g = 22.67 ± 0.07 R = 21.85 ± 0.05 The g-band magnitude is marginally consistent with the SDSS magnitude (Malesani et al., GCN 10621) of g = 22.89 ± 0.17, and suggests that the UVOT flattening (Marshall et al., GCN 10720) is primarily due to the host galaxy, not an associated supernova. Our reported R-band magnitude is significantly brighter than the host, but this excess is consistent with an afterglow origin (Bikmaev et al., GCN 10726). Additional follow-up observations will be necessary to comment on the presence (or absence) of a supernova counterpart.