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On rapid interstellar scintillation of quasars: PKS 1257-326 revisited

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2012
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Conference Paper

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Bignall, Hayley E. and Hodgson, Jeffery A. 2012. On rapid interstellar scintillation of quasars: PKS 1257-326 revisited, in Griffin R.E., Hanisch R.J., Seaman, R.L. (ed), 285th Symposium of the International-Astronomical-Union, Sep 19 2011, pp. 129-132. St Catherine's College, Oxford, England: Cambridge University Press.
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New Horizons in Time-Domain Astronomy
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285th Symposium of the International-Astronomical-Union
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Published in Proceedings of the International Astronomical Union 2012

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Abstract

The line of sight towards the compact, radio loud quasar PKS 1257-326 passesthrough a patch of scattering plasma in the local Galactic ISM that causes large and rapid,intra-hour variations in the received flux density at centimetre wavelengths. This rapid interstellarscintillation (SS) has been occurring for at least 15 years, implying that the scattering“screen” is at least 100 AU in physical extent. Through observations of the ISS we have measuredmicroarcsecond-scale “core shifts” in PKS 1257-326, corresponding to changing opacityduring an intrinsic outburst. Recent analysis of VLA data of a sample of 128 quasars found 6sources scintillating with a characteristic time-scale of < 2 hours, suggesting that nearby scatteringscreens in the ISM may have a covering fraction of a few percent. That is an importantconsideration for proposed surveys of the transient and variable radio sky