Abstract
Abstract The current understanding of the characteristics of solar and inner heliospheric electron events is inferred almost entirely from observations made by spacecraft located at 1 astronomical unit (au). Previous observations within 1 au of the Sun, by the Helios spacecraft at ∼0.3–1 au, indicate the presence of electron events that are not detected at 1 au or may have merged during transport from the Sun. Parker Solar Probe’s close proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of electrons with energies between ∼17 keV and ∼1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (IS⊙IS) instrument suite during Encounter 2 (2019 March 31–April 10 with perihelion of ∼0.17 au), including several small electron events. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe. We find most of these electron enhancements to be associated with type III radio emissions that reach the local plasma frequency and one enhancement that appears to be primarily associated with abrupt changes in the local magnetic field. Together, these associations suggest that these are indeed the first measurements of energetic electron events within 0.2 au.
Highlights
Energetic electron enhancements have been observed in situ since the earliest observations in the 1960s (e.g., Arnoldy et al 1960; Hoffman et al 1962; Frank 1965; Van Allen & Krimigis 1965; Anderson & Lin 1966) made with spacecraft such as Pioneer 5, Explorer 12, Explorer 14, Mariner 4, IMP-1, and IMP3
The association between radio bursts that extend to the local plasma frequency and a corresponding enhancement in the electron signals in both Energetic Particle Instruments (EPI)-Hi and EPI-Lo suggests that the Integrated Science Investigation of the Sun (ISeIS) telescopes are observing solar electron events
We presented the first observations of energetic electron events within 0.2 au of the Sun during Parker Solar Probe’s second encounter
Summary
Energetic electron enhancements have been observed in situ since the earliest observations in the 1960s (e.g., Arnoldy et al 1960; Hoffman et al 1962; Frank 1965; Van Allen & Krimigis 1965; Anderson & Lin 1966) made with spacecraft such as Pioneer 5, Explorer 12, Explorer 14, Mariner 4, IMP-1, and IMP3. Higher-energy solar electrons (>10–15 keV) are frequently observed to be delayed with respect to the lower energy electrons responsible for the type III radio emission (Krucker et al 1999; Haggerty & Roelof 2002; Klassen et al 2002; Cane 2003; Wang et al 2006, 2016). We present the first measurements of energetic electrons within 0.2 au, made around Parker Solar Probe’s second perihelion pass on 2019 April 4 (DOY 94) These tiny events have peak intensities of ∼1 cm−2 sr−1 s−1 MeV−1 for EPI-Hi (∼0.5–1 MeV) and ∼2 × 103 cm−2 sr−1 s−1 MeV−1 for EPILo (∼17–400 keV) and durations of less than one hour. We take advantage of statistical techniques and contemporaneous radio, magnetic fields, and plasma data measured by instruments on board Parker Solar Probe to attempt to identify real electron events that stand out above the background and may be the result of solar or inner heliospheric acceleration processes
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