  We describe the dynamics of an antiferromagnetic nano-oscillator in an
external magnetic field of any given time distribution. The oscillator is
powered by a spin current originating from spin-orbit effects in a neighboring
heavy metal layer, and is capable of emitting a THz signal in the presence of
an additional easy-plane anisotropy. We derive an analytical formula describing
the interaction between such a system and an external field, which can affect
the output signal character. Interactions with magnetic pulses of different
shapes, with a sinusoidal magnetic field and with a sequence of rapidly
changing magnetic fields are discussed. We also perform numerical simulations
based on the Landau-Lifshitz-Gilbert equation with spin-transfer torque effects
to verify the obtained results and find a very good quantitative agreement
between analytical and numerical predictions.
