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The space experiment CoRoT has recently detected transits by a hot Jupiteracross the disc of an active G7V star (CoRoT-Exo-2a) that can be considered asa good proxy for the Sun at an age of approximately 0.5 Gyr. We present a spotmodelling of the optical variability of the star during 142 days ofuninterrupted observations performed by CoRoT with unprecedented photometricprecision. We apply spot modelling approaches previously tested in the case ofthe Sun by modelling total solar irradiance variations. To model the lightcurve of CoRoT-Exo-2a, we take into account both the photometric effects ofcool spots as well as those of solar-like faculae, adopting solar analogy. Twoactive longitudes initially on opposite hemispheres are found on thephotosphere of CoRoT-Exo-2a with a rotation period of 4.522 $\pm$ 0.024 days.Their separation changes by approximately 80 degrees during the time span ofthe observations. From this variation, a relative amplitude of the surfacedifferential rotation lower than about 1 percent is estimated. Individual spotsform within the active longitudes and show an angular velocity about 1 percentsmaller than that of the longitude pattern. The total spotted area shows acyclic oscillation with a period of 28.9 $\pm$ 4.3 days, which is close to 10times the synodic period of the planet as seen by the rotating activelongitudes. The implications of such results for the internal rotation ofCoRoT-Exo-2a are discussed on the basis of solar analogy. A possible magneticstar-planet interaction is suggested by the cyclic variation of the spottedarea. Alternatively, the 28.9-d cycle may be related to Rossby-type wavespropagating in the subphotospheric layers of the star.

Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star