  Gravitationally bound clumps of dark matter axions in the form of
'miniclusters' or even denser 'axion stars' can generate strong radio signals
through axion-photon conversion when encountering highly magnetised neutron
star magnetospheres. We systematically study encounters of axion clumps with
neutron stars and characterise the axion infall, conversion and the subsequent
propagation of the photons. We show that the high density and low escape
velocity of the axion clumps lead to strong, narrow, and temporally
characteristic transient radio lines with an expected duration varying from
seconds to months. Our work comprises the first end-to-end modeling pipeline
capable of characterizing the radio signal generated during these transient
encounters, quantifying the typical brightness, anisotropy, spectral width, and
temporal evolution of the radio flux. The methods developed here may prove
essential in developing dedicated radio searches for transient radio lines
arising from miniclusters and axion stars.
