GCN Circular 9537
S. Dado and A. Dar report: The inferred photon spectral index Gamma=2.01+/-0.05 of the early time X-ray afterglow of the relatively nearby bright GRB090618 (z=1.54, GCN 9518) from the Swift XRT observations (Evans et al. http://www.swift.ac.uk/xrt_spectra/00355083/) implies, in the CB model (e.g. ApJ 696 (2009), 994), an asymptotic achromatic power-law decline of the afterglow with a spectral index beta=1.01+/-0.05 and a temporal index alpha=beta+1/2=1.51+/-0.05. The R-band light curve of the anticipated underlying supernova akin to SN1998bw is expected to reach maximum brightness magnitude R=23.9 (Galactic extinction included) around July 10, 2009 (approximately 22 days after GRB090618). Using the latest optical measurements reported in GCN 9531 and GCN 9536, the GRB afterglow is expected to decay by July 10, 2009 to a magnitude R=24.6+/-0.20 yielding R=23.4+/-0.3 for the optical transient superposed on a bright host galaxy with r=22.7 +/- 0.3 (GCN 9526). Like in the case of GRB 030319 (ApJ 594 (2003), L89), the search for an underlying supernova (GCN 9526) in GRB060618 may be more successful using large telescopes with high resolution for photometric and/or spectroscopic follow up measurements of its optical afterglow.