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Physical constraints on the sources of fast radio bursts are few, and therefore viable theoretical models are many. However, no one model can match all the available observational characteristics, meaning that these radio bursts remain one of the most mysterious phenomena in astrophysics.

Radio pulsars scintillate because their emission travels through the ionized interstellar medium along multiple paths, which interfere with each other. It has long been realized that, independent of their nature, the regions responsible for the scintillation could be used as ‘interstellar lenses’ to localize pulsar emission regions 1 , 2 . Most such lenses, however, resolve emission components only marginally, limiting results to statistical inferences and detections of small positional shifts 3 – 5 . As lenses situated close to their source offer better resolution, it should be easier to resolve emission regions of pulsars located in high-density environments such as supernova remnants 6 or binaries in which the pulsar’s companion has an ionized outflow. Here we report observations of extreme plasma lensing in the ‘black widow’ pulsar, B1957+20, near the phase in its 9.2-hour orbit at which its emission is eclipsed by its companion’s outflow 7 – 9 . During the lensing events, the observed radio flux is enhanced by factors of up to 70–80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and we infer a resolution of our lenses that is comparable to the pulsar’s radius, about 10 kilometres. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses 10 . Radiation from the ‘black widow’ pulsar B1957+20 is amplified when a companion brown dwarf passes in front of the source, suggesting that plasma flowing from the companion acts as a lens.

Fast radio burst FRB 110523, discovered in archival data, reveals Faraday rotation and scattering that suggests dense magnetized plasma near the source; this means that to infer the source of the burst, models should involve young stellar populations such as magnetars. A fast radio burster characterized An analysis of magnetization and scintillation data from the fast radio burst FRB 110523, discovered in archival data, provides clues about the environment of the burst — and its distance from us. Fast radio bursts are relatively newly discovered phenomena that have yet to be explained. They emit non-repeating, broadband, millisecond flashes and appear to originate from distant parts of the Universe and from objects only hundreds of kilometres in size or less. The new data from FRB 110523 reveal Faraday rotation and scattering that suggest dense magnetized plasma near the source, favouring models involving young stellar populations such as magnetars. Fast radio bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source 1 , 2 , 3 , 4 , 5 , 6 , 7 . The inferred all-sky burst rate 8 is comparable to the core-collapse supernova rate 9 out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1 (refs 10 and 11 ). These parameters are consistent with a wide range of source models 12 , 13 , 14 , 15 , 16 , 17 . One fast burst 6 revealed circular polarization of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in the fast radio burst FRB 110523. Its radio flux and dispersion measure are consistent with values from previously reported bursts and, accounting for a Galactic contribution to the dispersion and using a model of intergalactic electron density 10 , we place the source at a maximum redshift of 0.5. The burst has a much higher rotation measure than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. The detection in this instance of magnetization and scattering that are both local to the source favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low-density regions of the host galaxy.

Astrophysical techniques have pioneered the discovery of neutrino mass properties. Currently, the known neutrino effects on the large-scale structure of the Universe are all global, and neutrino masses are constrained by attempting to disentangle the small neutrino contribution from the sum of all matter using precise theoretical models. We investigate an alternative approach: to detect the difference between the neutrinos and that of dark matter and baryons. Here, by using one of the largest N -body simulations yet, we discover the differential neutrino condensation effect: in regions of the Universe with different neutrino relative abundance (the local ratio of neutrino to cold dark matter density), halo properties are different and neutrino mass can be inferred. In ‘neutrino-rich’ regions, more neutrinos can be captured by massive halos compared with ‘neutrino-poor’ regions. This effect differentially skews the halo mass function and opens up the path to independent measurements of neutrino mass in current or future galaxy surveys. Coevolving millions of cold dark matter particles and neutrinos within one N-body simulation, TianNu, shows that regions of similar dark matter density can have different neutrino densities. These density variations may have an effect on the cosmic structure.

Fast Radio Bursts (FRBs) are bright millisecond-duration radio transients that appear about 1000 times per day, all-sky, for a fluence threshold 5 Jy ms at 600 MHz. The FRB radio-emission physics and the compact objects involved in these events are subjects of intense and active debate. To better constrain source models, the Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is optimized to discover and localize a large sample of rare, high-fluence, and nearby FRBs. This population is the most amenable to multi-messenger and multi-wavelength follow-up, which allows a deeper understanding of source mechanisms. BURSTT will provide horizon-to-horizon sky coverage with a half power field-of-view (FoV) of ∼10 4 deg 2 , a 400 MHz effective bandwidth between 300 and 800 MHz, and subarcsecond localization, which is made possible using outrigger stations that are hundreds to thousands of km from the main array. Initially, BURSTT will employ 256 antennas. After tests of various antenna designs and optimizing the system’s performance, we plan to expand to 2048 antennas. We estimate that BURSTT-256 will detect and localize ∼100 bright (≥100 Jy ms) FRBs per year. Another advantage of BURSTT’s large FoV and continuous operation will be its greatly enhanced monitoring of FRBs for repetition. The current lack of sensitive all-sky observations likely means that many repeating FRBs are currently cataloged as single-event FRBs.

The directions of the galaxy angular momenta can be predicted from the initial conditions of the early Universe through the tidal torque. In simulations, these directions are well preserved through cosmic time, consistent with expectations of angular momentum conservation. We find evidence, statistically significant at ~2.7 σ , of correlation between observed oriented directions of galaxy angular momentum vectors and their predictions based on the initial density field reconstructed from the positions of Sloan Digital Sky Survey galaxies. This study presents evidence for a correlation between directions of galaxy angular momenta and cosmic initial conditions, and opens a way to use measurements of galaxy spins to probe fundamental physics in the early Universe. The observed oriented directions of galaxy angular momentum vectors correlate with predicted directions based on the initial density field reconstructed from the positions of Sloan Digital Sky Survey galaxies, opening a way to probe fundamental physics in the early Universe.

A broad view of the cosmos To study the past effects of cosmic dark energy — the force hypothesized to explain the increasing rate of expansion of the Universe — astronomers need to know more about the structure at extreme cosmological distances. The 21-centimetre radio emission line by neutral hydrogen is seen as a potentially useful tool for the purpose. Until now, 21-cm emission has been detected in galaxies only to a redshift of z = 0.24. Beyond this point, galaxies are too faint to be detected individually, but it is possible to measure the aggregate emission from many unresolved sources in the 'cosmic web'. Using the Green Bank Telescope in West Virginia, Chang et al . have produced a three-dimensional intensity map of hydrogen 21-cm radiation at redshifts of 0.53 to 1.12. Adding the H I emissions from the volumes surrounding about 10,000 galaxies from the DEEP2 optical galaxy redshift survey to the data set provides a view of the aggregate 21-cm glow to a statistical significance of 4σ. Hitherto, 21-cm emission has been detected in galaxies only to redshift 0.24, although it is possible to measure the aggregate emission from many more distant, unresolved sources in the 'cosmic web'. Here the authors report a three-dimensional 21-cm intensity field at redshift 0.53–1.12. They co-add neutral-hydrogen emission from the volumes surrounding about 10,000 galaxies to detect the aggregate 21-cm glow at a significance of approximately four standard deviations. Observations of 21-cm radio emission by neutral hydrogen at redshifts z  ≈ 0.5 to ∼2.5 are expected to provide a sensitive probe of cosmic dark energy 1 , 2 . This is particularly true around the onset of acceleration at z  ≈ 1, where traditional optical cosmology becomes very difficult because of the infrared opacity of the atmosphere. Hitherto, 21-cm emission has been detected 3 only to z = 0.24. More distant galaxies generally are too faint for individual detections but it is possible to measure the aggregate emission from many unresolved galaxies in the ‘cosmic web’. Here we report a three-dimensional 21-cm intensity field at z = 0.53 to 1.12. We then co-add neutral-hydrogen (H  i) emission from the volumes surrounding about 10,000 galaxies (from the DEEP2 optical galaxy redshift survey 4 ). We detect the aggregate 21-cm glow at a significance of ∼4 σ .

The Tianlai Cylinder Pathfinder is a radio interferometer array designed to test techniques for 21 cm intensity mapping in the post-reionization Universe, with the ultimate aim of mapping the large scale structure and measuring cosmological parameters such as the dark energy equation of state. Each of its three parallel cylinder reflectors is oriented in the north-south direction, and the array has a large field of view. As the Earth rotates, the northern sky is observed by drift scanning. The array is located in Hongliuxia, a radio-quiet site in Xinjiang, and saw its first light in September 2016. In this first data analysis paper for the Tianlai cylinder array, we discuss the sub-system qualification tests, and present basic system performance obtained from preliminary analysis of the commissioning observations during 2016-2018. We show typical interferometric visibility data, from which we derive the actual beam profile in the east-west direction and the frequency band-pass response. We describe also the calibration process to determine the complex gains for the array elements, either using bright astronomical point sources, or an artificial on site calibrator source, and discuss the instrument response stability, crucial for transit interferometry. Based on this analysis, we find a system temperature of about 90 K, and we also estimate the sensitivity of the array.

NRC publication: Yes