  We present photometry of the extrasolar planet WASP-5b in the 3.6 and 4.5
micron bands taken with the Spitzer Space Telescope's Infrared Array Camera as
part of the extended warm mission. By examining the depth of the planet's
secondary eclipse at these two wavelengths, we can place joint constraints on
the planet's atmospheric pressure-temperature profile and chemistry. We measure
secondary eclipse depths of 0.197% +/- 0.028% and 0.227% +/- 0.025% in the 3.6
micron and 4.5 micron bands, respectively. Our observations are best matched by
models showing a hot dayside and, depending on our choice of model, a weak
thermal inversion or no inversion at all. We measure a mean offset from the
predicted center of eclipse of 0.078 +/- 0.032 hours, translating to
ecos(omega) = 0.0031 +/- 0.0013 and consistent with a circular orbit. We see no
evidence for any eclipse timing variations comparable to those reported in a
previous transit study.
