We present our analysis of the red-channel CoRoT data of extrasolar planet CoRoT-2b .
A deep secondary eclipse is detected at a level of 1.02 \pm 0.20 \times 10 ^ { -4 } , which suggests that all of the planet-signal detected previously in white light by Alonso et al .
( 2009 ) originates from the red channel .
CoRoT-2b is the coolest exoplanet that has been detected in the optical so far .
In contrast to the other planets , its measured brightness temperature of 2170 \pm 55 K is significantly higher than its maximum hemisphere-averaged effective day-side temperature .
However , it is not expected that a hot Jupiter radiates as a black body , and its thermal spectrum can deviate significantly from a Planck curve .
We present models of the planet/star flux ratio as function of wavelength , which are calculated for a T/P profile in radiative and hydrostatic equilibrium , using a self-consistent atmosphere code .
These are compared with the CoRoT detection , and with measurements at 4.5 and 8 \mu m from the Spitzer Space Telescope from Gillon et al .
( 2009 ) .
We estimate that reflected light contributes only at a 10 - 20 % level to the total optical eclipse depth .
The models allow for an ’ extra absorber ’ to be inserted at high altitude in the planet ’ s atmosphere .
This produces a thermal inversion layer , recently invoked to explain the photometric reversals and flux enhancements seen in some planets in the infrared .
In the 0.5 - 1.5 \mu m wavelength range , the model-spectra of planets with an extra absorber at high altitude , are relatively suppressed in flux compared to those without such absorber .
We therefore argue that , in contrast to the other exoplanets detected in the optical so far , CoRoT-2b may not exhibit a significant thermal inversion in its atmosphere , causing its optical brightness temperature to be boosted above its maximum effective day-side temperature .