The High Energy Telescope (HET) on the SolarOrbiter Mission: Overview and First Data

As part of the Energetic Particle Detector (EPD) suite onboard Solar Orbiter, the High Energy Telescope has been launched on its mission to the Sun on February 9, 2020, and has been measuring energetic particles since it was first switched on about two weeks after launch. Using their double-ended telescopes, the two HET units provide measurements of ions above 7 MeV/nuc and electrons above 300 keV in four viewing directions. HET observed several Solar Energetic Particle (SEPs) events during the cruise phase, including the first one with a broad energy coverage (up to ~100MeV) on 29 Nov 2020. Being the first larger SEP event in a phase of rising solar activity, these measurements have already attracted extensive attention of the community. Apart from the SEPs, the HET can be used to observe the Galactic cosmic radiation (GCR) and its temporal variation. The GCR measurements can be also utilized for the validation of the energy response of HET. The overall spectra observed by HET are as expected, except for calibration issues in some specific energy bins that we are still investigating. Finally, the HET also observed several Forbush Decreases (FD), i.e. cosmic ray decreases caused by CMEs and their embedded magnetic field. Here, the capabilities and data products of HET, as well as first measurements of SEPs, GCR and FDs are presented.&#160;

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Cosmic-ray propagation around the Sun: investigating the influence of the solar magnetic field on the cosmic-ray Sun shadow

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936306 ◽

2020 ◽

Vol 633 ◽

pp. A83

Author(s):

J. Becker Tjus ◽

P. Desiati ◽

N. Döpper ◽

H. Fichtner ◽

J. Kleimann ◽

...

Keyword(s):

Magnetic Field ◽

Solar Activity ◽

Solar Cycle ◽

Cosmic Rays ◽

Solar Magnetic Field ◽

Cosmic Ray ◽

High Energy ◽

High Solar Activity ◽

The Sun ◽

Theoretical Understanding

The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays being blocked and deflected by the Sun and its magnetic field, has been observed by various experiments, such as Argo-YBJ, Tibet, HAWC, and IceCube. Most notably, the shadow’s size and depth was recently shown to correlate with the 11-year solar cycle. The interpretation of such measurements, which help to bridge the gap between solar physics and high-energy particle astrophysics, requires a solid theoretical understanding of cosmic-ray propagation in the coronal magnetic field. It is the aim of this paper to establish theoretical predictions for the cosmic-ray Sun shadow in order to identify observables that can be used to study this link in more detail. To determine the cosmic-ray Sun shadow, we numerically compute trajectories of charged cosmic rays in the energy range of 5−316 TeV for five different mass numbers. We present and analyze the resulting shadow images for protons and iron, as well as for typically measured cosmic-ray compositions. We confirm the observationally established correlation between the magnitude of the shadowing effect and both the mean sunspot number and the polarity of the magnetic field during the solar cycle. We also show that during low solar activity, the Sun’s shadow behaves similarly to that of a dipole, for which we find a non-monotonous dependence on energy. In particular, the shadow can become significantly more pronounced than the geometrical disk expected for a totally unmagnetized Sun. For times of high solar activity, we instead predict the shadow to depend monotonously on energy and to be generally weaker than the geometrical shadow for all tested energies. These effects should become visible in energy-resolved measurements of the Sun shadow, and may in the future become an independent measure for the level of disorder in the solar magnetic field.

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Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field Line Braiding Model with Compound Injections

The Astrophysical Journal ◽

10.3847/1538-4357/ac3233 ◽

2022 ◽

Vol 924 (1) ◽

pp. 22

Author(s):

Fan Guo ◽

Lulu Zhao ◽

Christina M. S. Cohen ◽

Joe Giacalone ◽

R. A. Leske ◽

...

Keyword(s):

Magnetic Field ◽

Energetic Particle ◽

Radial Distance ◽

Solar Energetic Particle ◽

The Sun ◽

Ion Composition ◽

Source Regions ◽

Solar Energetic Particle Events ◽

Composition Ratios ◽

Inner Heliosphere

Abstract We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly variable over more than two orders of magnitude, even if the source ratio is at the nominal value. Assuming a 3He/4He source ratio of 10% in impulsive 3He-rich events and the same spatial offset of the source regions, the 3He/4He ratio at observation sites also vary considerably. The variability of the ion composition ratios depends on the radial distance, which can be tested by observations made at different radial locations. We discuss the implications of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.

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Energy spectra of carbon and oxygen - Predictions from HELIOS E6 for Solar Orbiter HET

10.5194/egusphere-egu2020-5027 ◽

2020 ◽

Author(s):

Johannes Marquardt ◽

Bernd Heber ◽

Robert Elftmann ◽

Robert Wimmer-Schweingruber

Keyword(s):

Energetic Particle ◽

Solar Minimum ◽

Cosmic Ray ◽

High Energy ◽

Energy Spectra ◽

Particle Detector ◽

Quiet Time ◽

Transport Models ◽

Galactic Cosmic Ray ◽

Insight Into

Anomalous cosmic rays (ACRs) are well-suited to probe the transport conditions of energetic particles in the innermost heliosphere. We revisit the HELIOS Experiment 6 (E6) data in view of the upcoming Solar Orbiter Energetic Particle Detector (EPD) suite that will perform measurements during a comparable solar minimum within the same distance.Adapting the HELIOS energy ranges for oxygen and carbon to the ones given by the High Energy Telescope (HET) allows us to determine predictions for the upcoming measurements but also to put constraints on particle transport models that provide new insight into the boundary conditions close to the Sun.We present here the adapted energy spectra of galactic cosmic ray (GCR) carbon and oxygen, as well as of ACR oxygen during solar quiet time periods between 1975 to 1977. Due to the higher energy threshold of HET in comparison to E6 gradients of about 20% at 15 MeV/nucleon are expected. The largest ACR gradient measured by E6 was obtained to be about 75% between 9 and 13 MeV/nucleon and 0.4 AU and 1 AU.

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ENERGETIC PARTICLES IN THE HELIOSPHERE

International Journal of Modern Physics A ◽

10.1142/s0217751x05029654 ◽

2005 ◽

Vol 20 (29) ◽

pp. 6621-6632 ◽

Cited By ~ 2

Author(s):

BERND HEBER

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Cosmic Rays ◽

Energetic Particle ◽

Current Knowledge ◽

Cosmic Ray ◽

Interplanetary Shock ◽

The Sun ◽

Local Interstellar Medium ◽

Cosmic Ray Flux

The heliosphere is the region around the Sun that is filled by the solar wind and its embedded magnetic field. The interaction of the supersonic solar wind with the local interstellar medium leads to a transition from supersonic to subsonic speeds at the heliospheric termination shock. The latter is regarded to be the source of the anomalous component of cosmic rays. Within the heliosphere "local" energetic particle sources, like the Sun and interplanetary shock waves contribute to the cosmic ray flux, too. At energies below a few GeV the observed galactic and anomalous cosmic ray intensities are modulated by the heliospheric magnetic field. In my contribution, both the current knowledge and hypotheses about modulation and the transport of cosmic rays in the heliosphere are reviewed.

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Distinguishing the Sources

Solar Energetic Particles - Lecture Notes in Physics ◽

10.1007/978-3-030-66402-2_3 ◽

2021 ◽

pp. 49-69

Author(s):

Donald V. Reames

Keyword(s):

Magnetic Field ◽

Energetic Particle ◽

Solar Energetic Particle ◽

Active Regions ◽

High Energy ◽

Injection Time ◽

Closed Loops ◽

Compact Source ◽

Time Profiles ◽

Onset Timing

AbstractOur discussion of history has covered many of the observations that have led to the ideas of acceleration by shock waves or by magnetic reconnection in gradual and impulsive solar energetic particle (SEP) events, respectively. We now present other compelling observations, including onset timing, SEP-shock correlations, injection time profiles, high-energy spectral knees, e/p ratios, and intensity dropouts caused by a compact source, that have helped clarify these acceleration mechanisms and sources. However, some of the newest evidence now comes from source-plasma temperatures. In this and the next two chapters, we will find that impulsive events come from solar active regions at ≈ 3 MK, controlling ionization states Q, hence A/Q, and, in most gradual events, shocks accelerate ambient coronal material from ≤1.6 MK. When SEPs are trapped on closed loops they supply the energy for flares. In addition to helping to define their own origin, SEPs also probe the structure of the interplanetary magnetic field.

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Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere – Extension of WASAVIES to Earth orbit

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2019006 ◽

2019 ◽

Vol 9 ◽

pp. A9 ◽

Cited By ~ 2

Author(s):

Tatsuhiko Sato ◽

Ryuho Kataoka ◽

Daikou Shiota ◽

Yûki Kubo ◽

Mamoru Ishii ◽

...

Keyword(s):

Energetic Particle ◽

Solar Energetic Particle ◽

Cosmic Ray ◽

Ground Level ◽

High Energy ◽

Extended Version ◽

High Energy Proton ◽

Dose Rates ◽

Energy Proton ◽

Galactic Cosmic Ray

Real-time estimation of cosmic-ray fluxes on satellite orbits is one of the greatest challenges in space weather research. Therefore, we develop a system for nowcasting and forecasting the galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes at any location in the magnetosphere and ionosphere during ground-level enhancement (GLE) events. It is an extended version of the WArning System for AVIation Exposure to SEP (WASAVIES), which can determine event profiles by using real-time data of the count rates of several neutron monitors (NMs) at the ground level and high-energy proton fluxes observed by Geostationary Operational Environmental Satellites (GOES) satellites. The extended version, called WASAVIES-EO, can calculate the GCR and SEP fluxes outside a satellite based on its two-line element (TLE) data. Moreover, organ absorbed-dose and dose-equivalent rates of astronauts in the International Space Station (ISS) can be estimated using the system, considering its shielding effect. The accuracy of WASAVIES-EO was validated based on the dose rates measured in ISS, as well as based on high-energy proton fluxes observed by POES satellites during large GLEs that have occurred in the 21st century. Agreement between the nowcast and forecast dose rates in ISS, especially in terms of their temporal structures, indicates the usefulness of the developed system for future mission operations.

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The Common Origin of High-energy Protons in Solar Energetic Particle Events and Sustained Gamma-Ray Emission from the Sun

The Astrophysical Journal ◽

10.3847/1538-4357/ac004f ◽

2021 ◽

Vol 915 (2) ◽

pp. 82

Author(s):

N. Gopalswamy ◽

S. Yashiro ◽

P. Mäkelä ◽

H. Xie ◽

S. Akiyama

Keyword(s):

Energetic Particle ◽

Gamma Ray ◽

Solar Energetic Particle ◽

High Energy ◽

Common Origin ◽

The Sun ◽

Solar Energetic Particle Events ◽

The Common ◽

Gamma Ray Emission

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Introducing the Sun and SEPs

Solar Energetic Particles - Lecture Notes in Physics ◽

10.1007/978-3-030-66402-2_1 ◽

2021 ◽

pp. 1-18

Author(s):

Donald V. Reames

Keyword(s):

Magnetic Field ◽

Solar Activity ◽

Solar Cycle ◽

Differential Rotation ◽

Coronal Mass Ejections ◽

Energetic Particle ◽

Solar Magnetic Field ◽

Solar Energetic Particle ◽

Active Regions ◽

The Sun

AbstractThe structure of the Sun, with its energy generation and heating, creates convection and differential rotation of the outer solar plasma. This convection and rotation of the ionized plasma generates the solar magnetic field. This field and its variation spawn all of the solar activity: solar active regions, flares, jets, and coronal mass ejections (CMEs). Solar activity provides the origin and environment for both the impulsive and gradual solar energetic particle (SEP) events. This chapter introduces the background environment and basic properties of SEP events, time durations, abundances, and solar cycle variations.

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