Interplanetary Scintillation with the Murchison Widefield Array
Publications (newest first):
- Morgan et al. (2019) Interplanetary Scintillation with the Murchison Widefield Array V: Performing an All-sky Survey of Compact Sources using Modern Low-frequency Radio Telescopes
- Sadler et al. (2019) Interplanetary Scintillation studies with the Murchison Wide-field Array IV: The hosts of sub-arcsecond compact sources at low radio frequencies.
- Chhetri et al. (2018b) Interplanetary Scintillation studies with the Murchison Wide-field Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162 MHz
- Chhetri et al. (2018a) Interplanetary scintillation studies with the Murchison Widefield Array – II. Properties of sub-arcsecond compact sources at low radio frequencies
- Morgan et al. (2018a) Interplanetary Scintillation with the Murchison Widefield Array – I: a sub-arcsecond survey over 900 deg2 at 79 and 158 MHz (Associated software can be found here).
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The above video of a small part of the sky, made using a specialised technique in radio imaging, shows the “twinkling” effect that is used to identify objects with sub-arcseond compact components. Object in the video that do not show scintillation may be a very large radio galaxies (such as this example). The video is sped up 4 times and is in a continuous loop.
What is this new technique?
Interplanetary scintillation (IPS) is the phenomenon of random fluctuations in intensity of distant compact object, smaller than an arc second, induced by the inhomogeneous structures in the constant wind emanating from the sun. The effect is very similar to the twinkling of the stars (but not planets or the moon) at night time, however, the twinkling is induced by earth’s atmosphere. The first discovery of IPS was made by Margaret Clarke (Clarke 1964).
At ICRAR-Curtin, the unique properties of the Murchison Widefield Array (the excellent instantaneous UV coverage and the wide field of view) have been combined with IPS to produce a very powerful technique that allows identification of objects with sub-arcsecond compact structures from thousands of objects within a very short time period. Sub-arcsecond scale angular resolution is important because the compact cores in active galaxies (the area around the supermassive black holes that give rise to massive radio galaxies) subtend sub-arcsecond angles. Currently at low frequencies finding out which objects contain sub-arcsecond scale components is difficult because the required angular resolution can only be achieved with Very Long Baseline Interferometry (VLBI). But VLBI is time consuming, especially when conducting surveys of large number of objects (imagine doing VLBI on over 300 000 objects detected in the GLEAM survey). With a 5 minute observation with the MWA, we can identify which objects have subarcsecond compact components from ~2500 objects. The wide field of view of MWA enables coverage of very large areas of the sky in a short period of time. One of our objective is to apply this technique to the widest part of the sky, providing a complementary high angular resolution catalogue to other recent catalogues at low frequencies.
This opens up new opportunities to study the astrophysical properties of compact objects from low radio frequencies, previously not possible at such large scales. Combined with high resolution studies from high frequencies, we can gain important insights into the properties of compact AGNs and other compact objects, and gain a better understanding of radio galaxies and their evolution.