Imaginary images and Stokes phenomena in the weak plasma lensing of coherent sources
Abstract
The study of astrophysical plasma lensing, such as in the case of extreme scattering events, has typically been conducted using the geometric limit of optics, neglecting wave effects. However, for the lensing of coherent sources such as pulsars and fast radio bursts, wave effects can play an important role. Asymptotic methods, such as the socalled Eikonal limit, also known as the stationary phase approximation, have been used to include firstorder wave effects; however, these methods are discontinuous at Stokes lines. Stokes lines are generic features of a variety of lens models, and are regions in parameter space where imaginary images begin to contribute to the overall intensity modulation of lensed sources. Using the mathematical framework of PicardLefschetz theory to compute diffraction integrals, we argue that these imaginary images contain as much information as their geometric counterparts, and may potentially be observable in data. Thus, weaklensing events where these imaginary images are present can be as useful for inferring lens parameters as stronglensing events in which multiple geometric images are present.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2021
 DOI:
 10.1093/mnras/stab2337
 arXiv:
 arXiv:2103.08687
 Bibcode:
 2021MNRAS.507.5390J
 Keywords:

 gravitational lensing: strong;
 waves;
 pulsars: general;
 radio continuum: ISM;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 doi:10.1093/mnras/stab2337