Context :

Aims : We use four observational data sets , mainly from the Rosetta mission , to constrain the activity pattern of the nucleus of comet 67P/Churyumov-Gerasimenko .

Methods : We develop a numerical model that computes the production rate and non-gravitational acceleration of the nucleus of comet 67P as a function of time , taking into account its complex shape with a shape model reconstructed from OSIRIS imagery .
We use this model to fit three observational data sets : the trajectory data from flight dynamics ; the rotation state , as reconstructed from OSIRIS imagery ; and the water production measurements from ROSINA , of 67P .
The two key parameters of our model , adjusted to fit the three data sets all together , are the activity pattern and the momentum transfer efficiency ( i.e. , the so-called “ \eta parameter ” of the non-gravitational forces ) .

Results : We find an activity pattern able to successfully reproduce the three data sets simultaneously .
The fitted activity pattern exhibits two main features : a higher effective active fraction in two southern super-regions ( \sim 10 % ) outside perihelion compared to the northern ones ( < 4 % ) , and a drastic rise of the effective active fraction of the southern regions ( \sim 25 - 35 % ) around perihelion .
We interpret the time-varying southern effective active fraction by cyclic formation and removal of a dust mantle in these regions .
Our analysis supports moderate values of the momentum transfer coefficient \eta in the range 0.6 - 0.7 ; values \eta \leq 0.5 or \eta \geq 0.8 degrade significantly the fit to the three data sets .
Our conclusions reinforce the idea that seasonal effects linked to the orientation of the spin axis play a key role in the formation and evolution of dust mantles , and in turn largely control the temporal variations of the gas flux .

Conclusions :