Interstellar scintillation as a probe of microarcsecond scale structure in quasars

TL;DR

This paper discusses how interstellar scintillation (ISS) can be used as a tool to investigate microarcsecond-scale structures in quasars and properties of the interstellar medium, based on recent observations and surveys.

Contribution

It demonstrates the use of ISS observations to probe quasar inner jet structures and Galactic turbulence, highlighting recent findings on rapidly scintillating quasars.

Findings

ISS causes rapid flux variations in flat-spectrum radio sources.

Most scintillating sources are rare, requiring long-term monitoring.

Recent observations of PKS 1257-326 reveal intra-hour scintillation phenomena.

Abstract

Observations over the last two decades have shown that a significant fraction of all flat-spectrum, extragalactic radio sources exhibit flux density variations on timescales of a day or less at frequencies of several GHz. It has been demonstrated that interstellar scintillation (ISS) is the principal cause of such rapid variability. Observations of ISS can be used to probe very compact, microarcsecond-scale structure in quasar inner jets, as well as properties of turbulence in the local Galactic ISM. A few sources show unusually rapid, intra-hour variations, evidently due to scattering in very nearby, localized turbulence. We present recent findings for the rapidly scintillating quasar PKS 1257-326. The large-scale MASIV VLA Survey showed that such sources are extremely rare, implying that for most scintillating sources, longer-term, dedicated monitoring programs are required to extract detailed information on source structures.