We describe the motivation and design details of the ‘Phase II’ upgrade of the Murchison Widefield Array radio telescope. The expansion doubles to 256 the number of antenna tiles deployed in the array. The new antenna tiles enhance the capabilities of the Murchison Widefield Array in several key science areas. Seventy-two of the new tiles are deployed in a regular configuration near the existing array core. These new tiles enhance the surface brightness sensitivity of the array and will improve the ability of the Murchison Widefield Array to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ∼3.5. The remaining 56 tiles are deployed on long baselines, doubling the maximum baseline of the array and improving the arrayu, vcoverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floor of Murchison Widefield Array continuum images. The upgrade retains all of the features that have underpinned the Murchison Widefield Array’s success (large field of view, snapshot image quality, and pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.

We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio HII regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation; Type I shows no signature of massive star formation, Type II is associated with relatively small HII region(s) and Type III with both HII region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I GMCs do not host optically hidden HII regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in a sense they are located within ~100 pc of the molecular clouds. Among possible ideas to explain the GMC Types, we favor that the Types indicate an evolutionary sequence; i.e., the youngest phase is Type I, followed by Type II and the last phase is Type III, where the most active star formation takes place leading to cloud dispersal. The number of the three types of GMCs should be proportional to the time scale of each evolutionary stage if a steady state of massive star and cluster formation is a good approximation. By adopting the time scale of the youngest stellar clusters, 10 Myrs, we roughly estimate the timescales of Types I, II and III to be 6 Myrs, 13 Myrs and 7 Myrs, respectively, corresponding to a lifetime of 20-30 Myrs for the GMCs with a mass above the completeness limit, 5 x 10^4 Msun.

We present the first fully and uniformly sampled, spatially complete survey of the entire Magellanic System with high velocity resolution ( km s-1), performed with the Parkes Telescope. Approximately 24 percent of the southern sky was covered by this survey on a ≈5´ grid with an angular resolution of . A fully automated data-reduction scheme was developed for this survey to handle the large number of spectra (). The individual Hanning smoothed and polarization averaged spectra have an rms brightness temperature noise of σ = 0.12 K. The final data-cubes have an rms noise of K and an effective angular resolution of ≈16´. In this paper we describe the survey parameters, the data-reduction and the general distribution of the gas. The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are associated with huge gaseous features – the Magellanic Bridge, the Interface Region, the Magellanic Stream, and the Leading Arm – with a total mass of M() = , if all gas is at the same distance of 55 kpc. Approximately two thirds of this gas is located close to the Magellanic Clouds (Magellanic Bridge and Interface Region), and 25% of the gas is associated with the Magellanic Stream. The Leading Arm has a four times lower mass than the Magellanic Stream, corresponding to 6% of the total mass of the gaseous features. We have analyzed the velocity field of the Magellanic Clouds and their neighborhood introducing a LMC-standard-of-rest frame. The in the Magellanic Bridge shows low velocities relative to the Magellanic Clouds suggesting an almost parallel motion, while the gas in the Interface Region has significantly higher relative velocities indicating that this gas is leaving the Magellanic Bridge building up a new section of the Magellanic Stream. The Leading Arm is connected to the Magellanic Bridge close to an extended arm of the LMC. The clouds in the Magellanic Stream and the Leading Arm show significant differences, both in the column density distribution and in the shapes of the line profiles. The gas in the Magellanic Stream is more smoothly distributed than the gas in the Leading Arm. These morphological differences can be explained if the Leading Arm is at considerably lower z-heights and embedded in a higher pressure ambient medium.

Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning 17 months, which show that the FRB’s Faraday rotation is highly variable and twice changes sign. The FRB also depolarizes below radio frequencies of about 1 to 3 gigahertz. We interpret these properties as being due to changes in the parallel component of the magnetic field integrated along the line of sight, including reversing direction of the field. This could result from propagation through a turbulent magnetized screen of plasma, located 10 ^–5 to 100 parsecs from the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source.