Resonant $\gamma \to a$ transition in magnetar magnitosphere

The effect of a magnetized plasma on the resonant photoproduction of axions on the electromagnetic multipole components of the medium, $i\to f+a$, has been considered. It has been shown that the axion resonant emissivity, due to various reactions involving particles of the medium, is naturally expressed in terms of the emissivity of the photon $\to$ axion transition. The number of axions produced by the equilibrium cosmic microwave background radiation in the magnetar magnetosphere has been calculated. It has been shown that the resonant mechanism under consideration is inefficient for the production of cold dark mass.