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Multi‐point measurements on kinetic scales through Earth's magnetosheath have revealed a spectrum of filamentary currents and vortical flows advected with the shocked plasmas outside the magnetopause. The spectral energy density in these structures is correlated with enhanced ion temperatures. Using an empirically derived statistical model based on fluid‐kinetic theory for these structures we demonstrate how they act to scatter magnetosheath ions. Through the combined action of energization in the direction perpendicular to the background magnetic field along chaotic orbits, and pitch‐angle scattering into the parallel direction appreciable ion energization occurs. These dynamics drive heating while generating non‐thermal energetic tails similar to that observed. It is shown how the operation of this process depends on the field topology with deviations from planar form and counter‐propagation required to drive significant energization. This process will modulate ion anisotropies through the magnetosheath independent of both adiabatic effects and the action of anisotropy instabilities.

 

We analyze multipoint measurements in magnetosheath plasmas, just upstream of the Earth's magnetopause, to investigate the morphology of the turbulent fields and coincident 3‐D ion distributions observed. Using interferometric and generalized wave polarization analyses, we show how the fields comprise a multiscale spectrum of Alfvénic structures composed of flow shears and vortices, and current sheets and filaments advected over the spacecraft with the magnetosheath flow. It is shown how these features are correlated with intervals of enhanced ion energy, temperature anisotropy, and impulsive variations in the agyrotropy of ion velocity space distributions. It is demonstrated that the observed variation in ion properties is inconsistent with an adiabatic response but is instead correlated with the spectral energy density of nonplanar structures at ion gyroradii scales. The capacity of these field structures to scatter ions is considered.

 

Abstract A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at ∼7 MeV cm −2 (time period 1000 s) and ∼35 MeV cm −2 (time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total GW energy. These are the first limits on UHE photons from GW sources. 

Abstract We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above 10 19 eV. Photons in the zenith angle range from 30 ∘ to 60 ∘ can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95% CL are set to an E -2 diffuse flux of ultra-high energy photons above 10 19 eV, 2 × 10 19 eV and 4 × 10 19 eV amounting to 2.11 × 10 -3 , 3.12 × 10 -4 and 1.72 × 10 -4  km -2  sr -1  yr -1 , respectively. While the sensitivity of the present search around 2 × 10 19 eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated. 

Abstract In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above 6 × 10 17 eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around 5 × 10 18 eV (the so-called “ankle” feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources.To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs). 

Abstract A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 2004 January 1 and 2020 December 31 are given for cosmic rays that have energies in the range 78–166 EeV. Details are also given on a further nine very energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered.