Dual-Component Plasma Lens Models
  In contrast to the converging, achromatic behaviour of axisymmetric
gravitational lenses, diverging frequency-dependent lensing occurs from
refraction due to a distribution of over-dense axisymmetric plasma along an
observer's line of sight. Such plasma lenses are particularly interesting from
the point of view of astronomical observations because they can both magnify
and dim the appearance of background sources as a function of frequency. Plasma
lensing is believed to be involved in a number of separate phenomena involving
the scintillation of radio pulsars, extreme scattering events of background
radio sources and may also play a role in the generation of fast radio bursts.
These lensing phenomena are believed to occur in dense environments, in which
there may be many density perturbations between an observer and background
source. In this work we generalize individual plasma lens models to produce
dual component lenses using families of plasma lens models previously studied
in the literature, namely the exponential and softened power-law lenses.
Similar to binary gravitational lens models, these dual component plasma lenses
feature a rich and complex critical and caustic morphology, as well as generate
more complicated light curves. We map the number of criticals formed for a
given component separation and angular size, and highlight a relevant
degeneracy between two particular models. This work provides an argument in
favor of close monitoring of extreme scattering events in progress in order to
break such model degeneracies.
