Aims.
The Parker Solar Probe (PSP) orbit provides an opportunity to study the inner heliosphere at distances closer to the Sun than previously possible. Due to the solar minimum conditions, the ...initial orbits of PSP yielded only a few solar energetic particle (SEP) events for study. Recently during the fifth orbit, at distances from 0.45 to 0.3 au, the energetic particle suite on PSP, Integrated Science Investigation of the Sun (IS⊙IS), observed a series of six SEP events, adding to the limited number of SEP events studied inside of 0.5 au. Variations in the H and He spectra and the He/H abundance ratio are examined and discussed in relation to the identified solar source regions and activity.
Methods.
IS⊙IS measures the energetic particle environment from ~20 keV to >100 MeV/nuc. Six events were selected using the ~1 MeV proton intensities, and while small, they were sufficient to calculate proton and helium spectra from ~1 to ~10 MeV/nuc. For the three larger events, the He/H ratio as a function of energy was determined. Using the timing of the associated radio bursts, solar sources were identified for each event and the eruptions were examined in extreme ultraviolet emission.
Results.
The largest of the selected events has peak ~1 MeV proton intensities of 3.75 (cm
2
sr s MeV)
−1
. Within uncertainties, the He and H spectra have similar power law forms with indices ranging from −2.3 to −3.3. For the three largest events, the He/H ratios are found to be relatively energy independent; however, the ratios differ substantially with values of 0.0033 ± 0.0013, 0.177 ± 0.047, and 0.016 ± 0.009. An additional compositional variation is evident in both the
3
He and electron signatures. These variations are particularly interesting as the three larger events are likely a result of similar eruptions from the same active region.
Aims.
On 29 November 2020, at 12:34 UT, active region 12790 erupted with an M4.4 class flare and a 1700 km s
−1
coronal mass ejection. Parker Solar Probe (PSP) was completing its seventh orbit around ...the Sun and was located at 0.8 au when the Integrated Science Investigation of the Sun (IS⊙IS) measured the ensuing mid-sized solar energetic particle (SEP) event. Not only was this the first SEP event with heavy ions above 10 MeV nuc
−1
to be measured by IS⊙IS, it was also measured by several spacecraft positioned around the Sun, making it the first circumsolar event of solar cycle 25. Here we describe an overview of the SEP event characteristics at PSP.
Methods.
Fluence spectra for electrons, H, He, O, and Fe were calculated for the decay portion of the event. For the entire time period of the event, it was possible to calculate fluence spectra for electrons, O, and Fe only due to instrumental mode changes in one of the IS⊙IS telescopes, affecting H and He during the period of peak intensities. Using higher time resolution data, we also studied the onset of the event and temporal variations in the particle intensities at the shock and during the magnetic cloud passage.
Results.
During the decay, the ion spectra are consistent with power laws at low energies with an exponential rollover at a few MeV nuc
−1
, while the electron spectrum is consistent with a power law of index −5.3. Based on fits to the spectra, Fe/O and He/H abundance ratios as a function of energy are calculated and found to be nominal for large SEP events at hundreds of keV/nuc, but decrease strongly with increasing energy. The full-event spectra for O and Fe have similar shapes to those of the decay, but with higher roll-over energies. The electron spectrum for the full event is harder with an index of −3.4 and there is some evidence of higher energy components near ∼2 MeV and above ∼4 MeV. Despite the spacecraft being tilted 45° with respect to the nominal orientation of the spacecraft’s long axis pointed towards the Sun, there is some anisotropy apparent in MeV protons during the onset of the event. Velocity dispersion is also evident, consistent with a solar release time of 13:15 UT and pathlength of 1.3 au. The arrival of the related magnetic cloud resulted in the suppression of SEP intensities, although a brief increase in particle intensities suggests PSP moved out of the cloud for ∼30 min. This appears to be the first medium-sized event in the rise of cycle 25 activity, with additional large events likely to occur. Additional details of the event beyond this overview can be found in several related papers.
The Energetic Particle Instrument-Low Energy (EPI-Lo) experiment has detected several weak, low-energy (∼30-300 keV nucleon-1) solar energetic particle (SEP) events during its first two closest ...approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (IS IS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes retrograde motion, covering a 17° heliographic longitudinal range three times during the course of the ∼11-day perihelion passes, permitting a unique spatial and temporal study into the location, correlation, and persistence of previously unmeasurable SEPs. We examine the signatures of these SEPs (during the first PSP perihelion pass only) and the connection to possible solar sources using remote observations from the Solar Dynamics Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO), and the ground-based Global Oscillation Network Group (GONG). The orientation of the Sun relative to STEREO, SDO, and GONG makes such identifications challenging, but we do have several candidates, including an equatorial coronal hole at a Carrington longitude of ∼335°. To analyze observations from EPI-Lo, which is a new type of particle instrument, we examine instrumental effects and provide a preliminary separation of the ion signal from the photon background.
Abstract
On 2020 November 30, Parker Solar Probe (PSP) was crossed by a coronal mass ejection (CME)-driven shock, which we suggest was also crossing a convected, isolated magnetic structure (MS) at ...about the same time. By analyzing PSP/FIELDS magnetic field measurements, we find that the leading edge of the MS coincided with the crossing of the shock, while its trailing edge, identified as a crossing of a current sheet, overtook PSP about 7 minutes later. Prior to the arrival of the shock, the flux of 30 keV–3 MeV ions and electrons, as measured by PSP/Integrated Science Investigation of the Sun (ISOIS)/Energetic Particle Instrument (EPI-Lo), increased gradually, peaking at the time of the shock passage. However, during the crossing of the MS downstream of the shock, the energetic-ion flux dropped dramatically, before recovering at about the time of the crossing of the trailing edge of the MS. Afterwards, the ion fluxes remained approximately constant within the sheath region of the CME shock. We interpret this depletion of energetic ions within the MS as the result of insufficient time to accelerate particles at the shock within the MS, given that the structure moves along the shock surface owing to its advection with the solar wind. We present results from a quantitative numerical model of the interaction of an idealized MS with a shock, which supports this interpretation.
Abstract
Energetic electrons of Jovian origin have been observed for decades throughout the heliosphere, as far as 11 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 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 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.
Next-generation SOlar Neutron TRACking (SONTRAC) instrument de Nolfo, G.A.; Mitchell, J.G.; Suarez, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
September 2023, 2023-09-00, Letnik:
1054
Journal Article
Recenzirano
The SOlar Neutron TRACking (SONTRAC) instrument is a novel neutron spectrometer based on proton tracking. The instrument is composed of orthogonally-stacked 1 mm scintillating plastic fibers that are ...read out by commercially available high-resolution, fine-grain silicon photomultipliers (SiPMs). The fiber pitch is matched to the off-the-shelf 1.36 mm pitch of 8 × 8 arrays of 1 mm SiPMs from Broadcom. SiPM signals are readout by a 32-channel CAEN DT5550W readout system with the A55PET4 with front-end application-specific integrated circuits (ASICs; four Petiroc2 ASICs). The compact, low-power nature of the SiPM interface and ASIC readout translates to a realistic volume, power, and mass budget for a future SmallSAT or probe-class mission. The instrument prototype has been tested with laboratory radiation sources, ground-level muons, and a neutron/proton accelerator beam. We report on the instrument design and performance.
Abstract
At the end of 2020 November, two coronal mass ejections (CMEs) erupted from the Sun and propagated through the interplanetary medium in the direction of Parker Solar Probe while the ...spacecraft was located at ∼0.81 au. The passage of these interplanetary CMEs (ICMEs) starting on November 29 (DOY 334) produced the largest enhancement of energetic ions and electrons observed by the Integrated Science Investigation of the Sun (IS⊙IS) energetic particle instrument suite on board Parker Solar Probe during the mission’s first eight orbits. This was also the first spatially widespread solar energetic particle event observed in solar cycle 25. We investigate several key characteristics of the energetic electron event including the time profile and anisotropy distribution of near-relativistic electrons as measured by IS⊙IS’s low-energy Energetic Particle Instrument (EPI-Lo) and compare these observations with contextual data from the Parker Solar Probe Fields Experiment magnetometer. These are the first electron anisotropy measurements from IS⊙IS/EPI-Lo, demonstrating that the instrument can successfully produce these measurements. We find that the electron count rate peaks at the time of the shock driven by the faster of the two ICMEs, implying that the shock parameters of this ICME are conducive to the acceleration of electrons. Additionally, the angular distribution of the electrons during the passage of the magnetic clouds associated with the ICMEs shows significant anisotropy, with electrons moving primarily parallel and antiparallel to the local magnetic field as well as bidirectionally, providing an indication of the ICME’s magnetic topology and connectivity to the Sun or magnetic structures in the inner heliosphere.
Issue Title: The Composition of Matter We have measured the isotopic abundances of neon and a number of other species in the galactic cosmic rays (GCRs) using the Cosmic Ray Isotope Spectrometer ...(CRIS) aboard the ACE spacecraft. Our data are compared to recent results from two-component (Wolf-Rayet material plus solar-like mixtures) Wolf-Rayet (WR) models. The three largest deviations of galactic cosmic ray isotope ratios from solar-system ratios predicted by these models, ^sup 12^C/^sup 16^O, ^sup 22^Ne/^sup 20^Ne, and ^sup 58^Fe/^sup 56^Fe, are very close to those observed. All of the isotopic ratios that we have measured are consistent with a GCR source consisting of 20% of WR material mixed with 80% material with solar-system composition. Since WR stars are evolutionary products of OB stars, and most OB stars exist in OB associations that form superbubbles, the good agreement of our data with WR models suggests that OB associations within superbubbles are the likely source of at least a substantial fraction of GCRs. In previous work it has been shown that the primary ^sup 59^Ni (which decays only by electron-capture) in GCRs has decayed, indicating a time interval between nucleosynthesis and acceleration of >10^sup 5^ y. It has been suggested that in the OB association environment, ejecta from supernovae might be accelerated by the high velocity WR winds on a time scale that is short compared to the half-life of ^sup 59^Ni. Thus the ^sup 59^Ni might not have time to decay and this would cast doubt upon the OB association origin of cosmic rays. In this paper we suggest a scenario that should allow much of the ^sup 59^Ni to decay in the OB association environment and conclude that the hypothesis of the OB association origin of cosmic rays appears to be viable. PUBLICATION ABSTRACT
We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope ...Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 <= Z <= 28 in the energy range approx. 50-550 MeV / nucleon. Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than approx. 7%, and the relative abundances changed by less than approx. 4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2sigma, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.
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