  We use the Spitzer Space Telescope to estimate the dayside thermal emission
of the exoplanet TrES-3 integrated in the 3.6, 4.5, 5.8, and 8.0 micron
bandpasses of the Infrared Array Camera (IRAC) instrument. We observe two
secondary eclipses and find relative eclipse depths of 0.00346 +/- 0.00035,
0.00372 +/- 0.00054, 0.00449 +/- 0.00097, and 0.00475 +/- 0.00046, respectively
in the 4 IRAC bandpasses. We combine our results with the earlier K band
measurement of De Mooij et al. (2009), and compare them with models of the
planetary emission. We find that the planet does not require the presence of an
inversion layer in the high atmosphere. This is the first very strongly
irradiated planet that does not have a temperature inversion, which indicates
that stellar or planetary characteristics other than temperature have an
important impact on temperature inversion. De Mooij & Snellen (2009) also
detected a possible slight offset in the timing of the secondary eclipse in K
band. However, based on our 4 Spitzer channels, we place a 3sigma upper limit
of |ecos(w)| < 0.0056 where e is the planets orbital eccentricity and w is the
longitude of the periastron. This result strongly indicates that the orbit is
circular, as expected from tidal circularization theory.
