Engineering topics
Publications and source records attributed to G. A. de Nolfo.
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Detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 GeV to 7.5 TeV are presented from over 7 years of observations with the CALorimetric Electron Telescope (CALET) on the International Space Station. The instrument, consisting of a charge detector, an imaging calorimeter, and a total absorption calorimeter with a total depth of 30 radiation lengths at normal incidence and a fine shower imaging capability, is optimized to measure the all-electron spectrum well into the TeV region. Because of the excellent energy resolution (a few percent above 10 GeV) and the outstanding e/p separation (10 5 ), CALET provides optimal performance for a detailed search of structures in the energy spectrum. The analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. By adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 TeV is achieved, with a residual proton contamination less than 10%. The observed energy spectrum becomes gradually harder in the lower energy region from around 30 GeV, consistently with AMS-02, but from 300 to 600 GeV it is considerably softer than the spectra measured by DAMPE and Fermi-LAT. At high energies, the spectrum presents a sharp break around 1 TeV, with a spectral index change from −3.15 to −3.91, and a broken power law fitting the data in the energy range from 30 GeV to 4.8 TeV better than a single power law with 6.9 sigma significance, which is compatible with the DAMPE results. The break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). We have fitted the spectrum with a model consistent with the positron flux measured by AMS-02 below 1 TeV and interpreted the electron+positron spectrum with possible contributions from pulsars and nearby sources. Above 4.8 TeV, a possible contribution from known nearby supernova remnants, including Vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis.
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Energetic electrons of Jovian origin have been observed for decades throughout the heliosphere, as far as 11 astronomical units (au), and as close as 0.5 au, from the Sun. The treatment of Jupiter as a continuously emitting point source of energetic electrons has made Jovian electrons a valuable tool in the study of energetic electron transport within the heliosphere. We present observations of Jovian electrons measured by the EPI-Hi instrument in the Integrated Science Investigation of the Sun (IS ʘ IS) instrument suite on Parker Solar Probe at distances within 0.5 au of the Sun. These are the closest measurements of Jovian electrons to the Sun, providing a new opportunity to study the propagation and transport of energetic electrons to the inner heliosphere. We also find periods of nominal connection between the spacecraft and Jupiter in which expected Jovian electron enhancements are absent. Several explanations for these absent events are explored, including stream interaction regions (SIRs) between Jupiter and Parker Solar Probe and the spacecraft lying on the opposite side of the heliospheric current sheet from Jupiter, both of which could impede the flow of the electrons. These observations provide an opportunity to gain a greater insight into electron transport through a previously unexplored region of the inner heliosphere.
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Context.Solar energetic particles (SEPs) with energy in the GeV range can propagate to Earth from their acceleration region near the Sun and produce ground level enhancements (GLEs). The traditional approach to interpreting and modelling GLE observations assumes particle propagation which is only parallel to the magnetic field lines of interplanetary space, that is, spatially 1D propagation. Recent measurements by PAMELA have characterised SEP properties at 1 AU for the∼100 MeV–1 GeV range at high spectral resolution. Aims. We model the transport of GLE-energy solar protons using a 3D approach to assess the effect of the heliospheric current sheet(HCS) and drifts associated to the gradient and curvature of the Parker spiral. We derive 1 AU observables and compare the simulation results with data from PAMELA. Methods. We use a 3D test particle model including a HCS. Monoenergetic populations are studied first to obtain a qualitative picture of propagation patterns and numbers of crossings of the 1 AU sphere. Simulations for power law injection are used to derive intensity profiles and fluence spectra at 1 AU. A simulation for a specific event, GLE 71, is used for comparison purposes with PAMELA data. Results. Spatial patterns of 1 AU crossings and the average number of crossings per particle are strongly influenced by 3D effects, with significant differences between periods of A+ and A−polarities. The decay time constant of 1 AU intensity profiles varies depending on the position of the observer and it is not a simple function of the mean free path as in 1D models. Energy dependent leakage from the injection flux tube is particularly important for GLE energy particles, resulting in a rollover in the spectrum.
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