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Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that are visible at distances of billions of light years1. The nature of their progenitors and their emission mechanism remain open astrophysical questions2. Here we report the detection of the multicomponent FRB 20191221A and the identification of a periodic separation of 216.8(1) ms between its components, with a significance of 6.5σ. The long (roughly 3 s) duration and nine or more components forming the pulse profile make this source an outlier in the FRB population. Such short periodicity provides strong evidence for a neutron-star origin of the event. Moreover, our detection favours emission arising from the neutron-star magnetosphere3,4, as opposed to emission regions located further away from the star, as predicted by some models5.

Fast radio bursts (FRBs) are flashes of unknown physical origin1. The majority of FRBs have been seen only once, although some are known to generate multiple flashes2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. Recently, the discovery6of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths6. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.

We report the discovery of a faint Hαpulsar wind nebula (PWN) powered by the radio pulsar B0740-28. The characteristic bow-shock morphology of the PWN implies a direction of motion consistent with the previously measured velocity vector for the pulsar. The PWN has a flux density more than an order of magnitude lower than for the PWNe seen around other pulsars, but, for a distance 2 kpc, it is consistent with propagation through a medium of atomic density $n_{\rm H} \sim 0.25$cm-3, and neutral fraction of 1%. The morphology of the PWN in the area close to the pulsar is distinct from that in downstream regions, as is also seen for the PWN powered by PSR B2224+65. In particular, the PWN associated with PSR B0740–28 appears to close at its rear, suggesting that the pulsar has recently passed through a transition from low density to high density ambient gas. The faintness of this source underscores that deep searches are needed to find further examples of optical pulsar nebulae.

Ionization of the Earth's atmosphere by sunlight forms a complex, multilayered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide‐angle observation of an extensive array of field‐aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground‐based imaging technique. We establish their heights and motions by feature tracking and parallax analysis. The structures are strikingly organized, appearing as regularly spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures. Vast arrays of regularly spaced, field‐aligned ducts are common at midlatitudesWidefield, low‐frequency radio telescopes are powerful probes of the ionosphereNew imaging technique allows regional‐scale monitoring of plasma dynamics in 3‐D

The Southern Galactic Plane Survey (SGPS) is a 1.4 GHz radio polarization and H I survey in a large part of the inner Galactic plane at a resolution of about an arcmin. Depolarization and Faraday rotation of polarized radiation from diffuse Galactic synchrotron emission, pulsars, and extragalactic sources can be used to infer information about the strength and structure of the Galactic magnetic field. Here, we discuss early results of the polarization data from the SGPS. We show from statistical analysis of rotation measures of polarized extragalactic sources that fluctuations in the magnetoionized medium of the spiral arms are probably mainly caused by H II regions, while the rotation measure fluctuations in the interarm regions may be connected to the interstellar turbulent cascade. Furthermore, the variations of rotation measure with Galactic longitude enable modeling of the large-scale component of the Galactic magnetic field, including determination of the number and location of magnetic field reversals. Finally, the SGPS is an excellent way to study subparsec-scale structure in the ionized interstellar medium by way of depolarization studies in H II regions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic fields are a fundamental part of many astrophysical phenomena, but the evolution, structure and origin of magnetic fields are still unresolved problems in physics and astrophysics. When and how were the first fields generated? Are present-day magnetic fields the result of standard dynamo action, or do they represent rapid or recent field amplification through other processes? What role do magnetic fields play in turbulence, cosmic ray acceleration and structure formation? I explain how the Square Kilometre Array (SKA), a next-generation radio telescope, can deliver stunning new data-sets that will address these currently unanswered issues. The foundation for these experiments will be an all-sky survey of rotation measures, in which Faraday rotation toward > 107 background sources will provide a dense grid for probing magnetism in the Milky Way, nearby galaxies, and in distant galaxies, clusters and protogalaxies. Using these data, we can map out the evolution of magnetized structures from redshifts z > 3 to the present, can distinguish between different origins for seed magnetic fields in galaxies, and can develop a detailed model of the magnetic field geometry of the intergalactic medium and of the overall Universe. In addition, the SKA will certainly discover new magnetic phenomena beyond what we can currently predict or imagine. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The development of the radio remnant of SN 1987A has been followed using the Australia Telescope Compact Array since its first detection in 1990 August. The remnant has been observed at four frequencies, 1.4, 2.4, 4.8, and 8.6 GHz, at intervals of 4–6 weeks since the first detection. These data are combined with the 843 MHz data set of Ball et al. (2001) obtained at Molonglo Observatory to study the spectral and temporal variations of the emission. These observations show that the remnant continues to increase in brightness, with a larger rate of increase at recent times. They also show that the radio spectrum is becoming flatter, with the spectral index changing from −0.97 to −0.88 over the 11 years. In addition, at roughly yearly intervals since 1992, the remnant has been imaged at 9 GHz using super-resolution techniques to obtain an effective synthesised beamwidth of about 0".5. The imaging observations confirm the shell morphology of the radio remnant and show that it continues to expand at ~3000 km s−1. The bright regions of radio emission seen on the limb of the shell do not appear to be related to the optical hot spots which have subsequently appeared in surrounding circumstellar material. Keywords: circumstellar matter — radio continuum: ISM — supernovae: individual (SN 1987A) — supernova remnants

AbstractThe development of the radio remnant of SN 1987A has been followed using the Australia Telescope Compact Array since its first detection in 1990 August. The remnant has been observed at four frequencies, 1.4, 2.4, 4.8, and 8.6 GHz, at intervals of 4–6 weeks since the first detection. These data are combined with the 843 MHz data set of Ball et al. (2001) obtained at Molonglo Observatory to study the spectral and temporal variations of the emission. These observations show that the remnant continues to increase in brightness, with a larger rate of increase at recent times. They also show that the radio spectrum is becoming flatter, with the spectral index changing from -0.97 to -0.88 over the 11 years. In addition, at roughly yearly intervals since 1992, the remnant has been imaged at 9 GHz using super-resolution techniques to obtain an effective synthesised beamwidth of about 0?.5. The imaging observations confirm the shell morphology of the radio remnant and show that it continues to expand at ˜3000 km s-1. The bright regions of radio emission seen on the limb of the shell do not appear to be related to the optical hot spots which have subsequently appeared in surrounding circumstellar material.

The Southern Galactic Plane Survey (SGPS) is an H Iand 1.4 GHz continuum survey of the fourth quadrant of the Galaxy at arcminute resolution. We present here results on linearly polarized continuum emission from an initial 28 deg2test region for the SGPS, consisting of 190 mosaicked pointings of the Australia Telescope Compact Array and covering the range 3255 < l< 3325, -05 < b< 35. Complicated extended structure is seen in linear polarization throughout the test region, almost all of which has no correlation with total intensity. We interpret the brightest regions of polarized emission as representing intrinsic structure in extended polarization, most likely originating in the Crux spiral arm at a distance of 3.5 kpc; fainter polarized structure is imposed by Faraday rotation in foreground material. Two large areas in the field are devoid of polarization. We argue that these voids are produced by foreground H IIregions in which the magnetic field is disordered on scales of ~0.1-0.2 pc. We also identify a depolarized halo around the H IIregion RCW 94, which we suggest results from the interaction of the H IIregion with a surrounding molecular cloud.

We present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325·5&deg; &lessequal;l &lessequal; 333·5&deg;; &minus;0·5&deg; &lessequal; b &lessequal; 3·5&deg;) were completed in December 1998. Single-dish observations of the full survey region (253&deg; &lessequal; l &lessequal; 358 &deg; &bar;b&bar; &lessequal; 1&deg;) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS H I data, with particular attention to the smallest- and largest-scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent H I shells. On the small scale, we note extremely compact, cold clouds seen in H I self-absorption. We explore how these two classes of objects probe opposite ends of the H I spatial power spectrum. Keywords: Galaxy &mdash; ISM: bubbles, clouds, structure

AbstractWe present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325·5° =l= 333·5°; -0·5° = b= 3·5°) were completed in December 1998. Single-dish observations of the full survey region (253° = l= 358 ° |b| = 1°) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS H Idata, with particular attention to the smallest-and largest-scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent H Ishells. On the small scale, we note extremely compact, cold clouds seen in H Iself-absorption. We explore how these two classes of objects probe opposite ends of the H Ispatial power spectrum.

AbstractBefore and after every 12 hour synthesis observation, the Molonglo Observatory Synthesis Telescope (MOST) measures the flux densities of ~5 compact extragalactic radio sources, chosen from a list of 55 calibrators. From 1984 to 1996, the MOST made some 58,000 such measurements. We have developed an algorithm to process this dataset to produce a light curve for each source spanning this thirteen-year period. We find that 18 of the 55 calibrators are variable, on time scales between one and ten years. There is the tendency for sources closer to the Galactic Plane to be more likely to vary, which suggests that the variability is a result of refractive scintillation in the Galactic interstellar medium. The sources with the flattest radio spectra show the highest levels of variability, an effect possibly resulting from differing orientations of the radio axes to the line of sight.

AbstractA recent study has indicated that a substantial fraction of young pulsars born in supernovae have travelled outside the boundaries of their corresponding shell supernova remnants. A simple model suggests that this should not be the case, implying either that some postulated pulsar/remnant associations are false, or that pulsars are particularly difficult to detect until they have emerged from their remnants.

We present Australia Telescope Compact Array observations of the supernova remnant (SNR) G309.2–00.6. In a 1.3‐GHz continuum image the remnant appears as a near‐circular shell, but with two brightened and distorted arcs of emission on opposite sides. H iabsorption against the SNR yields a distance in the range 5.4 to 14.1 kpc, corresponding to an age (1−20) × 103yr. On the basis of the morphology of the SNR we argue that it is a younger analogue of the W 50/SS 433 system, and that its unusual appearance is a result of opposed jets or outflows from a central source. A jet‐like feature and breaks in the shell can both be seen along the axis of proposed outflow, providing further support for this interpretation; the central source itself is not detected. The SNR may be interacting with the adjacent H iiregion RCW 80 through an extension of the proposed outflow beyond its shell. This would put the SNR at the lower limit of its distance range and would imply an age 4000 yr. We consider other SNRs similar to G309.2–00.6, and propose remnants whose shells are affected by jets as one of several classes of SNR from which the presence of a central source can be inferred.

We present high-resolution radio images at 1.4 GHz of two Galactic supernova remnants (SNRs), G003.8-00.3 (formerly G003.7-00.2) and G350.0-02.0 (formerly G350.0-01.8). Although the two objects are very different in appearance, in both cases the radio emission shows a clear bilateral (or "barrel") morphology for which the axis is parallel to the Galactic plane.

The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (?2.?5), sensitivity (a 1?goal of 70 ?Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. > ?40°), a total of 33 885 deg. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.