Dectection of Thermal Emission from WASP-3b

We report secondary eclipse detections of the transiting hot Jupiter WASP-3b at 3.6, 4.5 and 8.0μm using the Spitzer Space Telescope's Infrared Array Camera. We find planet-to-star flux ratios of 0.210^+0.043 _-0.029, 0.281^+0.012 _-0.011 and 0.332^+0.050 _-0.034% in the three bands respectively. Comparisons with 1D atmospheric models show these values strongly favour inefficient redistribution of heat around the planet and also favour the presence of a temperature inversion. In addition, WASP-3 probes the cut-off region of a proposed activity-inversion correlation and we find evidence of atmospheric differences between this system and a similarly active system, WASP-4.