A repeating fast radio burst

Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances(1-8). Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections(9). The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events(10). Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst(4). This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star(11,12)

The Giant Radio Array for Neutrino Detection (GRAND) Project

The GRAND project aims to detect ultra-high-energy neutrinos, cosmic rays and gamma rays, with an array of 200,000 radio antennas over 200,000km$^2$, split into ∼20 sub-arrays of ∼10,000km$^2$ deployed worldwide. The strategy of GRAND is to detect air showers above 10$^{17}$eV that are induced by the interaction of ultra-high-energy particles in the atmosphere or in the Earth crust, through its associated coherent radio-emission in the 50−200MHz range. In its final configuration, GRAND plans to reach a neutrino-sensitivity of ∼10$^{−10}$GeV cm$^{−2}$s$^{−1}$sr$^{−1}$ above 5×10$^{17}$eV combined with a sub-degree angular resolution. GRANDProto300, the 300-antenna pathfinder array, is planned to start data-taking in 2021. It aims at demonstrating autonomous radio detection of inclined air-showers, and study cosmic rays around the transition between Galactic and extra-Galactic sources. We present preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution

The Giant Radio Array for Neutrino Detection (GRAND) Project

The GRAND project aims to detect ultra-high-energy neutrinos, cosmic rays and gamma rays, with an array of 200,000 radio antennas over 200,000km$^2$, split into ∼20 sub-arrays of ∼10,000km$^2$ deployed worldwide. The strategy of GRAND is to detect air showers above 10$^{17}$\,eV that are induced by the interaction of ultra-high-energy particles in the atmosphere or in the Earth crust, through its associated coherent radio-emission in the 50−200\,MHz range. In its final configuration, GRAND plans to reach a neutrino-sensitivity of ∼10$^{−10}$GeVcm$^{−2}$s$^{−1}$sr$^{−1}$ above 5×10$^{17}$\,eV combined with a sub-degree angular resolution. GRANDProto300, the 300-antenna pathfinder array, is planned to start data-taking in 2021. It aims at demonstrating autonomous radio detection of inclined air-showers, and study cosmic rays around the transition between Galactic and extra-Galactic sources. We present preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution

Self-trigger radio prototype array for GRAND

The GRANDProto300 (GP300) array is a pathfinder for the Giant Radio Array for Neutrino Detection (GRAND) project. The deployment of the array, consisting of 300 antennas, will start in 2021 in a radio-quiet area of ~200 km2 near Lenghu (~3000 m a.s.l.) in China. Serving as a test bench, the GP300 array is expected to pioneer techniques of autonomous radio detection including identification and reconstruction of nearly horizontal cosmic-ray (CR) air showers. In addition, the GP300 array is at a privileged position to study the transition between Galactic and extragalactic origins of cosmic rays, due to its large effective area and the precise measurements of both energy and mass composition for CRs with energies ranging from 30 PeV to 1 EeV. Using the GP300 array we will also investigate the potential sensitivity for radio transients such as Giant Radio Pulses and Fast Radio Bursts in the 50-200 MHz range

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA

A real-time fast radio burst: Polarization detection and multiwavelength follow-up

Fast radio bursts (FRBs) are one of the most tantalizing mysteries of the radio sky; their progenitors and origins remain unknown and until now no rapid multiwavelength follow-up of an FRB has been possible. New instrumentation has decreased the time between observation and discovery from years to seconds, and enables polarimetry to be performed on FRBs for the first time. We have discovered an FRB (FRB 140514) in real-time on 2014 May 14 at 17:14:11.06 UTC at the Parkes radio telescope and triggered follow-up at other wavelengths within hours of the event. FRB 140514 was found with a dispersion measure (DM) of 562.7(6) cm-3 pc, giving an upper limit on source redshift of z ≲ 0.5. FRB 140514 was found to be 21 ± 7 per cent (3σ) circularly polarized on the leading edge with a 1σ upper limit on linear polarization <10 per cent. We conclude that this polarization is intrinsic to the FRB. If there was any intrinsic linear polarization, as might be expected from coherent emission, then it may have been depolarized by Faraday rotation caused by passing through strong magnetic fields and/or high-density environments. FRB 140514 was discovered during a campaign to re-observe known FRB fields, and lies close to a previous discovery, FRB 110220; based on the difference in DMs of these bursts and time-on-sky arguments, we attribute the proximity to sampling bias and conclude that they are distinct objects. Follow-up conducted by 12 telescopes observing from X-ray to radio wavelengths was unable to identify a variable multiwavelength counterpart, allowing us to rule out models in which FRBs originate from nearby (z < 0.3) supernovae and long duration gamma-ray bursts. © 2014 The Authors

Alfven: magnetosphere-ionosphere connection explorers

The aurorae are dynamic, luminous displays that grace the night skies of Earth’s high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth’s atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The “ideal magnetohydrodynamics” description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfvén concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planet

Dissociation of the peptide-MHC class I complex limits the binding rate of exogenous peptide

Soluble, single-chain molecules for two MHC class I alleles, H-2Kd and H-2Kb, were used to analyze the kinetics of antigenic peptide binding to MHC. After MHC preloading with radiolabeled or fluorescent peptides, the observed rate of MHC-peptide complex dissociation increased after addition of an excess of unlabeled competitor peptide. Although exogenous peptides conforming to the allele-specific motif were required for the enhanced complex dissociation to occur, the dissociation rate of the complex was independent of exogenous peptide concentration. Similarly, the association rate of exogenous peptides was independent of concentration, reflecting the presence of low affinity peptides in the binding sites of the recombinant MHC proteins; the sequences of these endogenous peptides conform to the consensus motif for the MHC allele studied. Finally, the association rate of exogenous peptide decreased when MHC molecules were preloaded with high affinity peptides, and the binding of labeled high affinity peptide to isolated recombinant MHC was faster than the subsequent dissociation observed in the presence of competitor peptide. Taken together, these results imply that the rate of exogenous peptide binding is limited by the dissociation rate of the previously bound peptides

Dissociation of the peptide-MHC class I complex limits the binding rate of exogenous peptide

Soluble, single-chain molecules for two MHC class I alleles, H-2Kd and H-2Kb, were used to analyze the kinetics of antigenic peptide binding to MHC. After MHC preloading with radiolabeled or fluorescent peptides, the observed rate of MHC-peptide complex dissociation increased after addition of an excess of unlabeled competitor peptide. Although exogenous peptides conforming to the allele-specific motif were required for the enhanced complex dissociation to occur, the dissociation rate of the complex was independent of exogenous peptide concentration. Similarly, the association rate of exogenous peptides was independent of concentration, reflecting the presence of low affinity peptides in the binding sites of the recombinant MHC proteins; the sequences of these endogenous peptides conform to the consensus motif for the MHC allele studied. Finally, the association rate of exogenous peptide decreased when MHC molecules were preloaded with high affinity peptides, and the binding of labeled high affinity peptide to isolated recombinant MHC was faster than the subsequent dissociation observed in the presence of competitor peptide. Taken together, these results imply that the rate of exogenous peptide binding is limited by the dissociation rate of the previously bound peptides