Observations of intrahour variable quasars: scattering in our Galactic neighbourhood
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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 µ as scales. A few quasars have been found to show large amplitude scintillations on unusually rapid, intrahour timescales. This has been shownto be due to weak scattering in very local Galactic ‘screens’, within a few tens of parsec of the Sun. The short variability timescales allowdetailed study of the scintillation properties in relatively short observation 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.
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Macquart, Jean-pierre; de Bruyn, A. (2009)We report the discovery of fast, frequency-dependent intensity variations from the scintillating intra-day variable quasar J1819+3845 at 21 cm which resemble diffractive interstellar scintillations observed in pulsars. ...
Rapid interstellar scintillation of PKS 1257-326: Two-station pattern time delays and constraints on scattering and microarcsecond source structureBignall, Hayley; Macquart, Jean-Pierre; Jauncey, D.; Lovell, J.; Tzioumis, A.; Kedziora-Chudczer, L. (2006)We report measurements of time delays of up to 8 minutes in the centimeter-wavelength variability patterns of the intrahour scintillating quasar PKS 1257326, as observed between the VLA and the ATCA on three separate ...
Rapid Variability and Annual Cycles in the Characteristic Timescale of the Scintillating Source PKS 1257-326Bignall, Hayley; Jauncey, D.; Lovell, J.; Tzioumis, A.; Kedziora-Chudczer, L.; Macquart, Jean-pierre; Tingay, Steven; Rayner, D.; Clay, R. (2003)Rapid radio intraday variability (IDV) has been discovered in the southern quasar PKS 1257326. Fluxdensity changes of up to 40% in as little as 45 minutes have been observed in this source, making it, along with PKS 0405385 ...