Radio variability and interstellar scintillation of blazars

Bignall, Hayley Emma

Radio variability and interstellar scintillation of blazars

dc.contributor.advisor	Clay, Roger William	en
dc.contributor.author	Bignall, Hayley Emma	en
dc.contributor.school	Physics	en
dc.date.issued	2003	en
dc.description.abstract	This thesis presents several observational studies based on radio variability and interstellar scintillation of extragalactic flat-spectrum radio sources. Such sources are commonly called blazars, a term used to describe the phenomenon observed when the jet of a radio-loud Active Galactic Nucleus (AGN) is directed towards the observer. These sources provide unique laboratories for studying the physics of relativistic jets. Observations of selected samples of blazars, made with the Australia Telescope Compact Array (ATCA) and the Australia Telescope Long Baseline Array are presented here. Statistics for long-term (months--years) and short-term (intraday) variability in both total and linearly polarized flux density at several frequencies are presented. The sensitivity and flux density measurement accuracy of the ATCA make it particularly useful for observations of intraday variability (IDV). Resolving the question of what is the mechanism for radio IDV was of great importance at the time this thesis was being undertaken, since if intrinsic, IDV implies extremely high brightness temperatures, far in excess of the Inverse Compton limit for incoherent synchrotron radiation. Most source models are fundamentally based on the assumption that the radiation from radio to optical, and sometimes soft X-ray, energies is produced by the incoherent synchrotron mechanism, so any result which challenges this has serious implications. There is now strong evidence that interstellar scintillation (ISS) is the principal cause of radio IDV, which substantially lowers the implied source brightness temperatures from those calculated assuming intrinsic variability. Some of the results presented in this thesis have made an important contribution to the paradigm shift from IDV to ISS, by showing unequivocally that the rapid IDV observed in PKS 1257-326 is a result of scintillation due to a nearby scattering screen in the ionised interstellar medium (ISM) of our Galaxy. This unusual source, serendipitously discovered during the course of my PhD, has also proved extremely valuable in showing that ISS can be used as a probe of microarcsecond-scale source structure and also of the local Galactic ISM. Such high angular resolution is not currently achievable even with space interferometer baselines.	en
dc.description.dissertation	Thesis (Ph.D.)--Physics, 2003.	en
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dc.identifier.uri	http://hdl.handle.net/2440/37907
dc.language.iso	en	en
dc.provenance	This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exception. If you are the author of this thesis and do not wish it to be made publicly available or If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals	en
dc.subject	radio astronomy, interferometry	en
dc.title	Radio variability and interstellar scintillation of blazars	en
dc.type	Thesis	en