  The rate of energy exchange of spatially localized and gravitationally bound
axion configurations with electromagnetic radiation is investigated in presence
of strong static magnetic field. Fully analytic treatment is achieved based on
variationally optimized separable spatio-temporal clump profiles. For dilute
axion stars the equation of the energy variation is reinterpreted as a rate
equation of the axion number. Its solutions hints to an asymptotic $\sim
t^{1/5}$ increase of the clump size.
