Back to Volume
Paper: Extreme Scattering Events and Symmetric Achromatic Variations
Monograph: 7, Science with a Next Generation Very Large Array
Page: 491
Authors: Vedantham, H. K.
Abstract: Radio variability in quasars has been seen on timescales ranging from days to years due to both intrinsic and propagation induced effects (Kellermann & Pauliny-Toth 1968; Rickett 1990). Although separating the two is not always straight-forward, observations of singular ‘events' in radio light curves have led to two compelling, and thus far unresolved mysteries in propagation induced variability— extreme scattering events (ESE) that are a result of plasma lensing by AU-scale ionized structures in the interstellar medium, and symmetric achromatic variability (SAV) that is likely caused by gravitational lensing by ≳ 103 M objects. Nearly all theoretical explanations describing these putative lenses have remarkable astrophysical implications. In this chapter we introduce these phenomena, state the unanswered questions and discuss avenues to answer them with a ∼ weekly-cadence flux-monitoring survey of 103–104 flat-spectrum radio quasars with the ngVLA.
Back to Volume