The 64-dish MeerKAT telescope was inaugurated in 2018 and has been conducting regular science operations since then. In the meantime, new observation modes have been under development. Spectral line modes are available, as well as L-, UHF- and S-band receivers. MeerKAT’s excellent sensitivity over a wide range of angular scales makes it an excellent choice for studies of HII regions, supernova remnants and planetary nebulae. In addition, an OH megamaser has been detected at z > 0.5 for the first time.

We report on the detection of source noise in the time domain at 162 MHz with the Murchison Widefield Array. During the observation, the flux of our target source Virgo A (M87) contributes only $\sim$1% to the total power detected by any single antenna; thus, this source noise detection is made in an intermediate regime, where the source flux detected by the entire array is comparable with the noise from a single antenna. The magnitude of source noise detected is precisely in line with predictions. We consider the implications of source noise in this moderately strong regime on observations with current and future instruments.

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 $60+$ 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 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 array u, v coverage. 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.

The future SKA1-Low radio telescope will be powerful enough to produce tomographic images of the 21-cm signal from the Epoch of Reionization. Here we address how to identify ionized regions in such data sets, taking into account the resolution and noise levels associated with SKA1-Low. We describe three methods of which one, superpixel oversegmentation, consistently performs best.

Maser theory continues to be driven by advances in observational techniques. Here, I consider the responses to VLBI with space-Earth baselines and cross-correlation spectroscopy (a re-consideration of coherence properties), routine observation in full-Stokes polarization (a re-casting of the polarization transfer equations), and long-term variability monitoring (3-D modelling of irregular domains).

We have detected [C I] 3P1–3P0 emissions in the gaseous debris disks of 49 Ceti and β Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C I] are found to resemble those of CO(J=3–2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks, and is likely formed by the photodissociation of CO. Assuming an optically thin [C I] emission with the excitation temperature ranging from 30 to 100 K, the column density of C is evaluated to be (2.2 ± 0.2) × 1017 and (2.5 ± 0.7) × 1016 cm−2 for 49 Ceti and β Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 ± 19 and 69 ± 42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H2 molecules in the gas disk; i.e., there is an appreciable contribution of secondary gas from dust grains.

A condensed summary of molecular cloud astrophysics is presented. Some examples of the power of combining near-IR and mm molecular line observations are given.

GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination + 25° at frequencies between 72 and 231 MHz, made with the MWA using a drift scan method that makes efficient use of the MWA’s very large field-of-view. We present the observation details, imaging strategies, and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40-kHz frequency resolution and 0.5-s time resolution; the second year using 10-kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing, and image weighting scheme. At 154 MHz, the image resolution is approximately 2.5 × 2.2/cos (δ + 26.7°) arcmin with sensitivity to structures up to ~ 10° in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA’s primary beam.

The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80–300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3-km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper, the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.

Bipolar molecular outflows have been observed and studied extensively in the past, but some recent observations of periodic variations in maser intensity pose new challenges. Even quasi-periodic maser flares have been observed and reported in the literature. Motivated by these data, we have tried to study situations in binary systems with specific attention to the two observed features, i.e., the bipolar flows and the variabilities in the maser intensity. We have studied the evolution of spherically symmetric wind from one of the bodies in the binary system, in the plane of the binary. Our approach includes the analytical study of rotating flows with numerical computation of streamlines of fluid particles using PLUTO code. We present the results of our findings assuming simple configurations, and discuss the implications.

New low frequency radio telescopes currently being built open up the possibility of observing the 21 cm radiation from redshifts 200 > z > 30, also known as the dark ages, see Furlanetto, Oh, & Briggs(2006) for a review. At these high redshifts, Cosmic Microwave Background (CMB) radiation is absorbed by neutral hydrogen at its 21 cm hyperfine transition. This redshifted 21 cm signal thus carries information about the state of the early Universe and can be used to test fundamental physics. The 21 cm radiation probes a volume of the early Universe on kpc scales in contrast with CMB which probes a surface (of some finite thickness) on Mpc scales. Thus there is many orders of more information available, in principle, from the 21 cm observations of dark ages. We have studied the constraints these observations can put on the variation of fundamental constants (Khatri & Wandelt(2007)). Since the 21 cm signal depends on atomic physics it is very sensitive to the variations in the fine structure constant and can place constraints comparable to or better than the other astrophysical experiments (Δα/α= < 10−5) as shown in Figure 1. Making such observations will require radio telescopes of collecting area 10 - 106 km2 compared to ~ 1 km2 of current telescopes, for example LOFAR. We should also expect similar sensitivity to the electron to proton mass ratio. One of the challenges in observing this 21 cm cosmological signal is the presence of the synchrotron foregrounds which is many orders of magnitude larger than the cosmological signal but the two can be separated because of their different statistical nature (Zaldarriaga, Furlanetto, & Hernquist(2004)). Terrestrial EM interference from radio/TV etc. and Earth&s ionosphere poses problems for telescopes on ground which may be solved by going to the Moon and there are proposals for doing so, one of which is the Dark Ages Lunar Interferometer (DALI). In conclusion 21 cm cosmology promises a large wealth of data and provides the only way to observe the redshift range between recombination and reionization.

We report the results of a blind search for 22 GHz water masers in two regions, covering approximately half a square degree, within the G 333.2–0.6 giant molecular cloud. The complete search of the two regions was carried out with the 26 m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7 GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7 GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are slightly less red than those associated with methanol masers. Statistical investigation of the properties of the 13CO and 1.2 mm dust clumps with and without associated water masers shows that the water masers are associated with the more massive, denser and brighter 13CO and 1.2 mm dust clumps. We present statistical models that can predict those 13CO and 1.2 mm dust clumps likely to have associated water masers.

I will discuss the search for galaxies and QSOs at the highest redshifts, out to the Epoch of Reionization. Observations in the submillimeter play a fundamental role in such searches, in particular once ALMA will become operational. I will focus on the properties of the molecular gas (the phase of the ISM out of which stars form) in the earliest systems as derived through observations in the millimetre and radio regime. These observations allow us to measure the reservoir of molecular gas and to constrain the physical properties and excitation of the gas. Resolved imaging of the host galaxies also allows us to derive first dynamical masses for these objects. Such mass determinations are critical to determine whether there is a possible evolution of the famous MBH–σbulge relation with redshift or not. Recent measurements in the QSO redshift record holder J1148+5251 (z= 6.42) provide evidence that the black hole in this system assembled before the stellar bulge.

The Long Wavelength Array (LWA) will be a new, open, user-oriented astronomical instrument operating in the relatively unexplored window from 20–80 MHz near arcsecond angular resolution and milliJansky sensitivity. Operated by the University of New Mexico on behalf of the Southwest Consortium (SWC) the LWA will provide a unique training ground for the next generation of radio astronomers. Students may also put skills learned on the LWA to work in computer science, electrical engineering, and the communications industry, among others. The development of the LWA will follow a phased build which benefits from lessons learned at each phase. Four university-based Scientific Testing and Evaluation (ST&E) teams with different areas of concentration: (i) high-resolution imaging and particle acceleration; (ii) wide-field imaging and large scale structures; (iii) ionospheric physics; and (iv) radio frequency interference (RFI) suppression and transient detection will provide the feedback needed to assure that science objectives are met as the build develops. Currently in its first year of construction funding, the LWA team is working on the design for the first station (see also Ray et al. 2006).

The new cutting edge technologies have opened the possibility of using digital spectrometers to probe the sky. With the sampling rate of $\sim$400 Msamples/s and the capability to digitally process data in real-time it is possible to get wideband spectra covering the frequencies in the range 0-200 MHz with the resolution of a few kHz. This presentation will show how such a spectrometer can be applied to the forward-scattering method of meteor detection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html