VLBA observations of a rare multiple quasar imaging event caused by refraction in the interstellar medium

Understand

We report on the first detection of the theoretically-predicted rare phenomenon of multiple parsec-scale imaging of an active galactic nucleus induced by refractive effects due to localized foreground electron density enhancements, e.g., in an AU-scale plasma lens(es) in the ionized component of the Galactic interstellar medium.

• We detected multiple imaging in the low galactic latitude (b=-2 deg) quasar 2023+335 from the 15.4 GHz MOJAVE observations when the source was undergoing an ESE.
• While the parsec-scale jet of the source normally extends along PA -20 deg, in the 28 May 2009 and 23 July 2009 images a highly significant multi-component pattern of secondary images is stretched out nearly along the constant galactic latitude line with a local PA 40 deg, indicating that the direction of relative motion of the plasma lens is close to orbital.
• Weaker but still detectable imaging patterns at similar position angles are sporadically manifest at several other epochs.