Interplanetary Scintillation with the Murchison Widefield Array I: A sub-arcsecond Survey over 900 square degrees at 79 and 158 MHz

TL;DR

This paper introduces a novel low-frequency radio survey technique using the Murchison Widefield Array to detect interplanetary scintillation across 900 square degrees, revealing many sources with sub-arcsecond components.

Contribution

Developed a synthesis imaging method for large-N low-frequency telescopes to image IPS variability over wide fields and validated it with new source catalogues.

Findings

Over 700 scintillating sources detected at 79 and 158 MHz.

Approximately one scintillating source per square degree.

Detected sources with flux densities as low as 110 mJy at 158 MHz.

Abstract

We present the first dedicated observations of Interplanetary Scintillation (IPS) with the Murchison Widefield Array (MWA). We have developed a synthesis imaging technique, tailored to the properties of modern "large-N" low-frequency radio telescopes. This allows us to image the variability on IPS timescales across 900 square degrees simultaneously. We show that for our observations, a sampling rate of just 2Hz is sufficient to resolve the IPS signature of most sources. We develop tests to ensure that IPS variability is separated from ionospheric or instrumental variability. We validate our results by comparison with existing catalogues of IPS sources, and near-contemporaneous observations by other IPS facilities. Using just five minutes of data, we produce catalogues at both 79MHz and 158MHz, each containing over 350 scintillating sources. At the field centre we detect approximately one scintillating source per square degree, with a minimum scintillating flux density at 158MHz of 110mJy, corresponding to a compact flux density of approximately 400mJy. Each of these sources is a known radio source, however only a minority were previously known to contain sub-arcsecond components. We discuss our findings and the prospects they hold for future astrophysical and heliospheric studies.