Observations of Intrahour Variable Quasars: Scattering in our Galactic Neighbourhood

TL;DR

This paper reviews how interstellar scintillation causes rapid, intrahour variability in certain quasars, enabling detailed study of local Galactic structures and the quasars themselves.

Contribution

It summarizes key observational results from three well-studied intrahour variable quasars, highlighting the role of local Galactic scattering screens.

Findings

ISS causes rapid quasar variability on intrahour timescales.

Local Galactic screens within tens of parsecs induce weak scattering.

Observations of these quasars help probe small-scale Galactic structures.

Abstract

Interstellar scintillation (ISS) has been established as the cause of the random variations seen at centimetre wavelengths in many compact radio sources on timescales of a day or less. Observations of ISS can be used to probe structure both in the ionized insterstellar medium of the Galaxy, and in the extragalactic sources themselves, down to microarcsecond scales. A few quasars have been found to show large amplitude scintillations on unusually rapid, intrahour timescales. This has been shown to be due to weak scattering in very local Galactic ``screens'', within a few tens of parsec of the Sun. The short variability timescales allow detailed study of the scintillation properties in relatively short observing periods with compact interferometric arrays. The three best-studied ``intrahour variable'' quasars, PKS 0405-385, J1819+3845 and PKS 1257-326, have been instrumental in establishing ISS as the principal cause of intraday variability at centimetre wavelengths. Here we review the relevant results from observations of these three sources.