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We report the first astrophysical application of the technique of wide-fieldInterplanetary Scintillation (IPS) with the Murchison Widefield Array (MWA).This powerful technique allows us to identify and measure sub-arcsecond compactcomponents in low-frequency radio sources across large areas of sky without theneed for long-baseline interferometry or ionospheric calibration. We presentthe results of a five-minute observation of a 30x30 sq. deg MWA field at 162MHz with 0.5 second time resolution. Of the 2550 continuum sources detected inthis field, 302 (12 per cent) show rapid fluctuations caused by IPS. We findthat at least 32% of bright low-frequency radio sources contain a sub-arcseccompact component that contributes over 40% of the total flux density. Perhapssurprisingly, peaked-spectrum radio sources are the dominant population amongthe strongly-scintillating, low-frequency sources in our sample. Whilegamma-ray AGN are generally compact, flat-spectrum radio sources at higherfrequencies, the 162 MHz properties of many of the Fermi blazars in our fieldare consistent with a compact component embedded within more extendedlow-frequency emission. The detection of a known pulsar in our field shows thatthe wide-field IPS technique is at the threshold of sensitivity needed todetect new pulsars using image plane analysis, and scaling the current MWAsensitivity to that expected for SKA-low implies that large IPS-based pulsarsearches will be feasible with SKA. Calibration strategies for the SKA requirea better knowledge of the space density of compact sources at low radiofrequencies, which IPS observations can now provide.

Interplanetary Scintillation studies with the Murchison Wide-field Array II: Properties of sub-arcsecond compact sources at low radio frequencies