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The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together
programs recorded 20 000 h producing 146 papers to date. In 2016, the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper, we review the major results from the prior operation of the MWA and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes but also include ideas for directions outside these categories.
We present techniques developed to calibrate and correct Murchison Widefield Array low-frequency (72–300 MHz) radio observations for polarimetry. The extremely wide field-of-view, excellent instantaneous (u, v)-coverage and sensitivity to degree-scale structure that the Murchison Widefield Array provides enable instrumental calibration, removal of instrumental artefacts, and correction for ionospheric Faraday rotation through imaging techniques. With the demonstrated polarimetric capabilities of the Murchison Widefield Array, we discuss future directions for polarimetric science at low frequencies to answer outstanding questions relating to polarised source counts, source depolarisation, pulsar science, low-mass stars, exoplanets, the nature of the interstellar and intergalactic media, and the solar environment.
A new set of equations describing the coupling of high-frequency electrostatic waves with ion fluctuations is obtained taking into account a non-thermal electron distribution. It is shown that there exist stationary envelope solitons which have qualitatively different structures from the solutions reported earlier. In particular, the Langmuir field envelopes are found with similar width and strong field intensities in comparison to the isothermal case. It is also shown that the presence of the fast or non-thermal electrons significantly modifies the nature of Langmuir solitons in the transition from a single-hump solution to a double-hump solution as the Mach number increases to unity. The low-frequency electrostatic potential associated with the high-frequency Langmuir field has the usual single-dip symmetric structure whose amplitude increases with increasing Mach number. Furthermore, the dip at the center of the double-hump Langmuir soliton is found to become smaller as the proportion of non-thermal electrons increases.
Most treatments of lower hybrid waves include either electromagnetic or warm-plasma effects, but not both. Here we compare numerical dispersion curves for lower hybrid waves with a new analytic dispersion relation that includes both warm and electromagnetic effects. Very good agreement is obtained over significant ranges in wavenumber and plasma parameters, except where ion magnetization effects become important.
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