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Pulsars make fabulous tools as probes of the interstellar medium (ISM) of our Galaxy. Their radiation is pulsed, spatially coherent and highly polarised – a combination which enables their signals to carry imprints of the ionised, turbulent and magneto-ionic properties of the media through which they propagate. At low radio frequencies (i.e. longer wavelengths), these effects are magnified as a result of strong dependencies of these effects with the observing frequency.
Multipath propagation through the ISM gives rise to a rich variety of observable effects, many of which can be meaningfully used to probe the smallest structures in interstellar turbulence. For decades, possible investigations were limited to the use of more traditional scattering and scintillation techniques, which are generally useful for a statistical characterisation of the ISM along the pulsar’s sight line. Deflected parts of the radiation may also occasionally give rise to subtle features in the secondary spectra of pulsar scintillation (e.g. parabolic arcs), and these can be exploited to pinpoint the location of turbulent plasma or probe any anisotropy that is present. A particularly exciting development has been the application of novel techniques such as cyclic spectroscopy (Demorest 2011), and phase-retrieval algorithms that enable coherent de-scattering; i.e. simultaneous recovery of the pulsar’s intrinsic signal and the signal delay structure of the ISM (Walker et al. 2013).
This project will capitalise on new instrumentation and capabilities that are now on the horizon for pulsar observations with the Murchison Widefield Array (MWA) and its sister facility, the Engineering Development Array (EDA). It will soon be possible to access fine time resolution (~microseconds) pulsar data with the future high time resolution capabilities of the MWA, and even finer time resolution (~nanoseconds) with the EDA. Development of the related instrumentation and signal processing and exploiting them for first science applications will form the central theme of the project. Potential new science include accurate characterisation of signal distortion due to the ISM and holographic reconstruction of the interstellar microstructure. The project will involve close collaboration with Univ. of Auckland (NZ) and Manly Astrophysics.

Dynamic scintillation spectrum of the millisecond pulsar J0437-4715 (left) and its secondary spectrum (right), from MWA observations (Bhat et al. 2016). Faint parabolic arc-like features arise from deflected parts of pulsar’s scattered radiation. Future capabilities at the MWA and EDA will provide very high time resolution pulsar data to enable detailed characterisations of the ISM effects.

Dynamic scintillation spectrum of the millisecond pulsar J0437-4715 (left) and its secondary spectrum (right), from MWA observations (Bhat et al. 2016). Faint parabolic arc-like features arise from deflected parts of pulsar’s scattered radiation. Future capabilities at the MWA and EDA will provide very high time resolution pulsar data to enable detailed characterisations of the ISM effects.

Co-Supervisor

Dr Steven Tremblay

Postdoctoral Fellow (CAASTRO)

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