  We report detection of thermal emission from the exoplanet WASP-19b at 3.6,
4.5, 5.8 and 8.0 micron. We used the InfraRed Array Camera on the Spitzer Space
Telescope to observe two occultations of WASP-19b by its host star. We combine
our new detections with previous measurements of WASP-19b's emission at 1.6 and
2.09 micron to construct a spectral energy distribution of the planet's dayside
atmosphere. By comparing this with model-atmosphere spectra, we find that the
dayside atmosphere of WASP-19b lacks a strong temperature inversion. As WASP-19
is an active star (log RHK = -4.50 +/- 0.03), this finding supports the
hypothesis of Knutson, Howard & Isaacson (2010) that inversions are suppressed
in hot Jupiters orbiting active stars. The available data are unable to
differentiate between a carbon-rich and an oxygen-rich atmosphere.
