Acceleration Of Energetic Electrons Research Articles

A Multipeak Solar Flare with a High Turnover Frequency of the Gyrosynchrotron Spectra from the Loop-top Source

The origin of multiple peaks in light curves of various wavelengths remains illusive during flares. Here we discuss the flare of SOL2023-05-09T03:54M6.5 with six flux peaks as recorded by a tandem of new microwave and hard X-ray (HXR) instruments. According to its microwave spectra, the flare represents a high-turnover-frequency (>15 GHz) event. The rather-complete microwave and HXR spectral coverage provides a rare opportunity to uncover the origin of such an event together with simultaneous EUV images. We concluded that (1) the microwave sources originates around the top section of the flaring loops with a trend of source spatial dispersion with frequency; (2) the visible movement of the microwave source from peak to peak originates from the process of new flaring loops appearing sequentially along the magnetic neutral line; (3) the optically thin microwave spectra are hard with the indices (α tn) varying from ∼−1.2 to −0.4, and the turnover frequency always exceeds 15 GHz; (4) higher turnover/peak frequency corresponds to stronger peak intensity and harder optically thin spectra. Using the Fokker–Planck and GX Simulator codes we obtained a good fit to the observed microwave spectra and spatial distribution of the sources at all peaks, if assuming the radiating energetic electrons have the same spatial distribution and single-power-law spectra but with the number density varying in a range of ∼30%. We conclude that the particle acceleration in this flare happens in a compact region nearing the loop-top. These results provide new constraints on the acceleration of energetic electrons and the underlying flare intermittent reconnection process.

Testing adiabatic models of energetic electron acceleration at dipolarization fronts

Betatron acceleration is commonly cited as a primary accelerator of energetic electrons at dipolarization fronts, and many case studies compare observed energetic electrons measurements to a betatron model. In this work, we extend this to a statistical study. We identified 168 dipolarizations with an enhanced flux of energetic electrons at Magnetospheric Multiscale (MMS). We compared the observed flux of energetic electrons above 1 keV to a betatron acceleration model assuming a source population similar to the population in the quiet plasma sheet and found that, on average, the model slightly overestimated the observation, but there was a wide spread of errors. We then tested characteristics such as position, change in and strength of magnetic field, and wave power to determine if any of these characteristics affected the accuracy of the model; the only clear correlations were that the model was less accurate when the initial total magnetic field was smaller and when there was a higher Ey during the dipolarization. Since the betatron model did not explain our observations very well, we repeated with a full adiabatic model that included a Fermi acceleration component as well. We found that the adiabatic model slightly underestimated the observations, but with a smaller error than the betatron model under the same assumptions. Testing the same parameters, we found that the adiabatic model also did not strongly rely on any of the parameters except the initial magnetic field, and the anti-correlation with Ey was no longer present. The fact that neither model was generally applicable means that either adiabatic processes alone are not enough to explain electron acceleration at dipolarization fronts in general, or the common assumption we used, that the source population has the same phase space density as the cold pre-existing population, is not valid.

Distribution and Evolution of Chorus Waves Modeled by a Neural Network: The Importance of Imbalanced Regression

AbstractWhistler‐mode chorus waves play an essential role in the acceleration and loss of energetic electrons in the Earth’s inner magnetosphere, with the more intense waves producing the most dramatic effects. However, it is challenging to predict the amplitude of strong chorus waves due to the imbalanced nature of the data set, that is, there are many more non‐chorus data points than strong chorus waves. Thus, traditional models usually underestimate chorus wave amplitudes significantly during active times. Using an imbalanced regressive (IR) method, we develop a neural network model of lower‐band (LB) chorus waves using 7‐year observations from the EMFISIS instrument onboard Van Allen Probes. The feature selection process suggests that the auroral electrojet index alone captures most of the variations of chorus waves. The large amplitude of strong chorus waves can be predicted for the first time. Furthermore, our model shows that the equatorial LB chorus’s spatiotemporal evolution is similar to the drift path of substorm‐injected electrons. We also show that the chorus waves have a peak amplitude at the equator in the source MLT near midnight, but toward noon, there is a local minimum in amplitude at the equator with two off‐equator amplitude peaks in both hemispheres, likely caused by the bifurcated drift paths of substorm injections on the dayside. The IR‐based chorus model will improve radiation belt prediction by providing chorus wave distributions, especially storm‐time strong chorus. Since data imbalance is ubiquitous and inherent in space physics and other physical systems, imbalanced regressive methods deserve more attention in space physics.

Multiple injections of energetic electrons associated with the flare and CME event on 9 October 2021

Context. We study the solar energetic particle (SEP) event observed on 9 October 2021 by multiple spacecraft, including Solar Orbiter. The event was associated with an M1.6 flare, a coronal mass ejection, and a shock wave. During the event, high-energy protons and electrons were recorded by multiple instruments located within a narrow longitudinal cone. Aims. An interesting aspect of the event was the multi-stage particle energisation during the flare impulsive phase and also what appears to be a separate phase of electron acceleration detected at Solar Orbiter after the flare maximum. We aim to investigate and identify the multiple sources of energetic electron acceleration. Methods. We utilised SEP electron observations from the Energetic Particle Detector (EPD) and hard X-ray (HXR) observations from the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter, in combination with radio observations at a broad frequency range. We focused on establishing an association between the energetic electrons and the different HXR and radio emissions associated with the multiple acceleration episodes. Results. We find that the flare was able to accelerate electrons for at least 20 min during the non-thermal phase, observed in the form of five discrete HXR pulses. We also show evidence that the shock wave contributed to the electron acceleration during and after the impulsive flare phase. The detailed analysis of EPD electron data shows that there was a time difference in the release of low- and high-energy electrons, with the high-energy release delayed. Also, the observed electron anisotropy characteristics suggest a different connectivity during the two phases of acceleration.

Two-step Acceleration of Energetic Electrons at Magnetic Flux Ropes during Turbulent Reconnection

Energetic electrons have been frequently observed during magnetic reconnection in the magnetotail. The acceleration process of the energetic electrons is not fully understood. In this paper, we select for a detailed study a case of energetic electron acceleration from the earlier reported interval of turbulent magnetic reconnection in Earth’s magnetotail observed by the Magnetospheric Multiscale mission. We use the first-order Taylor expansion method to reconstruct the magnetic topology of electron acceleration sites from the data. We find that the energetic electron fluxes increase inside the flux rope forming in front of the magnetic pileup region. We show that the energetic electrons are produced by a two-step process where two different acceleration mechanisms are successively operating outside and inside the flux rope. First, the thermal electrons are energized in the field-aligned direction inside the magnetic pileup region owing to the Fermi mechanism forming a cigar-like distribution. Second, those energized electrons are further accelerated predominately antiparallel to the magnetic field direction by a parallel electric field inside the flux rope. Our findings provide information for a better understanding of the generation of energetic electrons during turbulent reconnection process.

Numerical Modeling of Energetic Electron Acceleration, Transport, and Emission in Solar Flares: Connecting Loop-top and Footpoint Hard X-Ray Sources

The acceleration and transport of energetic electrons during solar flares is one of the outstanding topics in solar physics. Recent X-ray and radio imaging and spectroscopy observations have provided diagnostics of the distribution of nonthermal electrons and suggested that, in certain flare events, electrons are primarily accelerated in the loop top and likely experience trapping and/or scattering effects. By combining the focused particle transport equation with magnetohydrodynamic (MHD) simulations of solar flares, we present a macroscopic particle model that naturally incorporates electron acceleration and transport. Our simulation results indicate that physical processes such as turbulent pitch-angle scattering can have important impacts on both electron acceleration in the loop top and transport in the flare loop, and their influences are highly energy-dependent. A spatial-dependent turbulent scattering with enhancement in the loop top can enable both efficient electron acceleration to high energies and transport of abundant electrons to the footpoints. We further generate spatially resolved synthetic hard X-ray (HXR) emission images and spectra, revealing both the loop-top and footpoint HXR sources. Similar to the observations, we show that the footpoint HXR sources are brighter and harder than the loop-top HXR source. We suggest that the macroscopic particle model provides new insights into understanding the connection between the observed loop-top and footpoint nonthermal emission sources by combining the particle model with dynamically evolving MHD simulations of solar flares.

Pitch Angle Distribution of MeV Electrons in the Magnetosphere of Jupiter

AbstractThe magnetosphere of Jupiter harbors the most extreme fluxes of MeV electrons in the solar system and therefore provides a testbed of choice to understand the origin, transport, acceleration, and loss of energetic electrons in planetary magnetospheres. Along this objective, the Pitch Angle Distribution (PAD) of energetic electrons may reveal signatures of the dominant physical processes. Here, we analyze for the first time the PAD of MeV electrons observed by the Galileo‐Energetic Particle Detector (EPD) experiment in orbit around Jupiter from 1995 to 2003. We find that the MeV electron PADs observed by the integral channels of EPD appear relatively isotropic with a flux anisotropy lower than a factor of 3. Due to the relatively large angular apertures of the EPD telescopes, the actual anisotropy may be larger than the observed one. The fine anisotropy observed by Galileo‐EPD reveals persistent pancake distributions at the M‐shell of M = 9. Outward of this distance, at M = 15 and M = 20–60, MeV electron distributions have pancake, isotropic, and scattered beam field‐aligned distributions. The scattered beam distributions can either be evidence of outward adiabatic transport or may suggest that high‐latitude auroral acceleration can transiently supply as much trapped MeV electrons to the middle magnetosphere as the inward adiabatic transport of electrons from an outer equatorial reservoir.

Electron Energization by High‐Amplitude Turbulent Electric Fields: A Possible Source of the Outer Radiation Belt

AbstractThe turbulent energy cascade that is characteristic of bursty bulk flow (BBF) braking regions in the Earth's magnetotail has been shown to be the energy source of large‐amplitude electric fields (>50 mV/m) which can, in turn, result in local energetic electron acceleration. These pre‐energized electrons can move inward to stronger magnetic fields being further accelerated and can eventually supply an energetic tail to electron distributions in the outer radiation belt. Using wave and plasma measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites during four tail seasons from 2015 to 2019, we study the process of BBF magnetic and kinetic energy being transferred to electrons by turbulent electric fields from a statistical perspective. We identify turbulent BBF regions by the presence of high‐amplitude electric fields. We show that the high‐amplitude electric fields are associated with an increase in electron temperature by three times compared to quiet times and with a ten‐fold increase in temperature fluctuations. They are also associated with strong variations of energetic electron fluxes, indicative of local acceleration. We further discuss the implications of these findings and the role of this pre‐energized electron population in supplying the outer radiation belt.

Magnetospheric response to solar wind forcing: ultra-low-frequency wave–particle interaction perspective

Abstract. Solar wind forcing, e.g., interplanetary shock and/or solar wind dynamic pressure pulses impacting Earth's magnetosphere, manifests many fundamental important space physics phenomena, including producing electromagnetic waves, plasma heating, and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physics based on in situ spacecraft measurements, ground-based magnetometer data, magnetohydrodynamics (MHD) and kinetic simulations. Magnetosphere response to solar wind forcing is not just a “one-kick” scenario. It is found that after the impact of solar wind forcing on Earth's magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change in interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generation of a series of waves, including poloidal-mode ultra-low-frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contains two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression, (2) followed by the wave–particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. Generalized theory of drift and drift–bounce resonance with growth- or decay-localized ULF waves has been developed to explain in situ spacecraft observations. The wave-related observational features like distorted energy spectrum, “boomerang” and “fishbone” pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the framework of this generalized theory. It is worth pointing out here that poloidal ULF waves are much more efficient at accelerating and modulating electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune and other astrophysical objects with magnetic fields.

On the Role of Coronal Shocks for Accelerating Solar Energetic Electrons

Abstract We study the role of coronal mass ejection (CME) driven shocks in the acceleration of solar energetic electrons. Using observations by the two STEREO spacecraft, we correlate electron peak intensities of solar energetic particle events measured in situ with various parameters of the associated coronal shocks. These shock parameters were derived by combining 3D shock reconstructions with global modeling of the corona. This modeling technique provides also shock properties in the specific shock regions that are magnetically connected to the two STEREO spacecraft. We find significant correlations between the peak intensities and the Mach number of the shock with correlation coefficients of about 0.7, which are similar for electrons at ∼1 MeV and protons at >60 MeV. Lower-energy electrons with <100 keV show a smaller correlation coefficient of 0.47. The causal relationship between electron intensities and the shock properties is supported by the vanishing correlations when peak intensities at STEREO A are related with the Alfvénic Mach number at the magnetic footpoint of STEREO B and vice versa, which yields correlation coefficients of 0.03 and −0.13 for ∼1 MeV and <100 keV electron peak intensities, respectively. We conclude that the high-energy electrons are accelerated mainly by the shock, while the low-energy electrons are likely produced by a mixture of flare and shock-related acceleration processes.

Energy-dependent Boundaries of Earth's Radiation Belt Electron Slot Region

Abstract The variations in radiation belt boundaries reflect competition between acceleration and loss physical processes of energetic electrons, which is an important issue for radiation belts of planets with an internal magnetic field (e.g., Earth, Jupiter, and Saturn). Based on high-quality measurements from Van Allen Probes spanning the years 2014–2018, we develop an empirical model of the energy-dependent boundaries of Earth's electron radiation belt slot region, showing that the lower boundary follows a logarithmic function of the electron energy while the upper boundary is controlled by two competing energy-dependent processes, namely compression and recovery. The compression process relates linearly to a 15 hr averaged Kp index, while the recovery process is found to be approximately proportional to time. Detailed data-model comparisons demonstrate that our model, using only the Kp index and time epoch as inputs, reconstructs the slot region boundaries in real time for 200 keV to 2 MeV electrons under varying geomagnetic conditions. Such a data-driven empirical model is prerequisite to understanding the dynamic changes of the slot region in response to both solar and geomagnetic activities. The model can be readily incorporated into future global simulations of radiation belt electron dynamics in Earth's inner magnetosphere and provide new insights into the study of Saturn's and Jupiter's radiation belt variability.

Localized Acceleration of Energetic Particles by a Weak Shock in the Solar Corona

Abstract Globally propagating shocks in the solar corona have long been studied to quantify their involvement in the acceleration of energetic particles. However, this work has tended to focus on large events associated with strong solar flares and fast coronal mass ejections (CMEs), where the waves are sufficiently fast to easily accelerate particles to high energies. Here we present observations of particle acceleration associated with a global wave event which occurred on 2011 October 1. Using differential emission measure analysis, the global shock wave was found to be incredibly weak, with an Alfvén Mach number of ∼1.008–1.013. Despite this, spatially resolved type iii radio emission was observed by the Nançay RadioHeliograph at distinct locations near the shock front, suggesting localized acceleration of energetic electrons. Further investigation using magnetic field extrapolation identified a fan structure beneath a magnetic null located above the source active region, with the erupting CME contained within this topological feature. We propose that a reconfiguration of the coronal magnetic field driven by the erupting CME enabled the weak shock to accelerate particles along field lines initially contained within the fan and subsequently opening into the heliosphere, producing the observed type iii emission. These results suggest that even weak global shocks in the solar corona can accelerate energetic particles via reconfiguration of the surrounding magnetic field.

Connecting solar flare hard X-ray spectra to in situ electron spectra

Aims. We aim to constrain the acceleration, injection, and transport processes of flare-accelerated energetic electrons by comparing their characteristics at the Sun with those injected into interplanetary space. Methods. We have identified 17 energetic electron events well-observed with the SEPT instrument aboard STEREO which show a clear association with a hard X-ray (HXR) flare observed with the RHESSI spacecraft. We compare the spectral indices of the RHESSI HXR spectra with those of the interplanetary electrons. Because of the frequent double-power-law shape of the in situ electron spectra, we paid special attention to the choice of the spectral index used for comparison. Results. The time difference between the electron onsets and the associated type III and microwave bursts suggests that the electron events are detected at 1 AU with apparent delays ranging from 9 to 41 min. While the parent solar activity is clearly impulsive, also showing a high correlation with extreme ultraviolet jets, most of the studied events occur in temporal coincidence with coronal mass ejections (CMEs). In spite of the observed onset delays and presence of CMEs in the low corona, we find a significant correlation of about 0.8 between the spectral indices of the HXR flare and the in situ electrons. The correlations increase if only events with significant anisotropy are considered. This suggests that transport effects can alter the injected spectra leading to a strongly reduced imprint of the flare acceleration. Conclusions. We conclude that interplanetary transport effects must be taken into account when inferring the initial acceleration of solar energetic electron events. Although our results suggest a clear imprint of flare acceleration for the analyzed event sample, a secondary acceleration might be present which could account for the observed delays. However, the limited and variable pitch-angle coverage of SEPT could also be the reason for the observed delays.

On the horizontal currents over the Martian magnetic cusp

Localized crustal magnetization over heavily cratered southern hemisphere at Mars gives rise to open magnetic field configurations which interact with the solar wind magnetic field to form magnetic cusp. The downward acceleration of energetic electrons in these cusps can produce aurora and an extended topside ionospheric structure over regions of magnetic anomalies. We report plasma collisions with the neutral atmosphere at one of the Martian cusps located at 82 o S and 180 o E, where the crustal field is strong with a radial component ~35° from the local zenith. We find that the dynamo region in the upper ionosphere of Mars is located between altitudes of 102 km and 210 km. The electrons in this region are constrained to gyrate along magnetic field lines while ions are dragged by neutrals and move along the direction of applied force. In the absence of the electric field, the horizontal current in the Martian dynamo is generated by the differential motion of ions and electrons. We find that the bulk of the current density is equatorward and confined within the Martian dynamo near the ionospheric peak with a magnitude of ~3.5 µA/m 2 . We also find that the eastward current density of magnitude ~0.4 µA/m 2 peaking near the upper boundary of the Martian dynamo is generated by magnetized ions in the F × B direction.

Cluster Observations of Energetic Electron Acceleration Within Earthward Reconnection Jet and Associated Magnetic Flux Rope

AbstractWe study acceleration of energetic electrons in an earthward plasma jet due to magnetic reconnection in the Earth magnetotail for one case observed by Cluster. The case has been selected based on the presence of high fluxes of energetic electrons, Cluster being in the burst mode and Cluster separation being around 1,000 km that is optimal for studies of ion scale physics. We show that two characteristic acceleration mechanisms are operating during this event. First, significant acceleration is achieved inside the magnetic flux pile‐up of the jet, the acceleration mechanism being consistent with betatron acceleration. Second, strong energetic electron acceleration occurs in magnetic flux rope like structure forming in front of the magnetic flux pile‐up region. Energetic electrons inside the magnetic flux rope are accelerated predominantly in the field‐aligned direction and the acceleration can be due to Fermi acceleration in a contracting flux rope.

Energetic Electron Enhancement and Dropout Echoes Induced by Solar Wind Dynamic Pressure Decrease: The Effect of Phase Space Density Profile

AbstractThe interplanetary (IP) shock with the sudden increase of solar wind dynamic pressure can cause the acceleration and transportation of energetic electrons in the inner magnetosphere. In this study, we further examine the influence of the sudden drop of solar wind dynamic pressure on magnetospheric energetic particles, through case study of energetic electron drift echoes and statistics with 25 cases from 2012 to 2017. We found that there were both dropout and enhancement drift echoes of electrons in some dynamic pressure decrease events, while other events only show electron dropout drift echoes. In addition, we analyzed the electron phase space density (PSD) and found that the radial profile of electron PSD were different for the two types of events, suggesting that the electron PSD plays an important role in the variations of energy electron fluxes induced by the dynamics pressure decrease. The results of this study, combined with previous studies of energetic electron dynamics caused by IP shocks, can provide a more general picture of both solar wind dynamic pressure decrease and increase effects on the energetic electrons.

Study of Spatiotemporal Development of Global Distribution of Magnetospheric ELF/VLF Waves Using Ground‐Based and Satellite Observations, and RAM‐SCB Simulations, for the March and November 2017 Storms

AbstractMagnetospheric Extremely Low‐Frequency/Very Low‐Frequency (ELF/VLF) waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave‐particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave‐particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground‐based stations at subauroral latitudes, Exploration of energization and Radiation in Geospace and RBSP satellites, POES/MetOp satellites, and the RAM‐SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 h. Ground observations tend not to observe ELF/VLF waves in the post‐midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post‐midnight sector.

Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging Spectroscopy

Abstract Nonthermal sources located above bright flare arcades, referred to as the “above-the-loop-top” sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the Expanded Owens Valley Solar Array and the Reuven Ramaty High Energy Solar Spectroscopic Imager, respectively. By combining the microwave and HXR imaging spectroscopy observations with multifilter extreme ultraviolet and soft X-ray imaging data, we derive the coronal magnetic field and energetic electron distribution of the source over a broad energy range from <10 keV up to ∼MeV during the early impulsive phase of the flare. The source has a strong magnetic field of over 800 G. The best-fit electron distribution consists of a thermal “core” from ∼25 MK plasma. A nonthermal power-law “tail” joins the thermal core at ∼16 keV with a spectral index of ∼3.6, which breaks down at above ∼160 keV to >6.0. Temporally resolved analysis suggests that the electron distribution above the break energy rapidly hardens with the spectral index decreasing from >20 to ∼6.0 within 20 s, or less than ∼10 Alfvén crossing times in the source. These results provide strong support for the above-the-loop-top source as the primary site where an ongoing bulk acceleration of energetic electrons is taking place very early in the flare energy release.

The FRB–SGR connection

ABSTRACT The discovery that the Galactic Soft Gamma Repeater (SGR) 1935+2154 emitted Fast Radio Burst (FRB) 200428 simultaneous with a gamma-ray flare, demonstrated the common source and association of these phenomena. If FRB radio emission is the result of coherent curvature radiation, the net charge of the radiating ‘bunches’ or waves may be inferred from the radiated fields, independent of the mechanism by which the bunches are produced. A statistical argument indicates that the radiating bunches must have a Lorentz factor ⪆ 10. The observed radiation frequencies indicate that their phase velocity (pattern speed) corresponds to Lorentz factors ⪆ 100. Coulomb repulsion implies that the electrons making up these bunches have yet larger Lorentz factors, limited by their incoherent curvature radiation. These electrons also Compton scatter the soft gamma-rays of the SGR. In FRB 200428, the power they radiated coherently at radio frequencies exceeded that of Compton scattering, but in more luminous SGR outbursts, Compton scattering dominates, precluding the acceleration of energetic electrons. This explains the absence of a FRB associated with the giant 2004 December 27 outburst of SGR 1806−20. SGR with luminosity ≳ 1042 erg s–1 are predicted not to emit FRB, while those of lesser luminosity can do so. ‘Superbursts’ like FRB 200428 are produced when narrowly collimated FRB are aligned with the line of sight; they are unusual, but not rare, and ‘cosmological’ FRB may be superbursts.

Global Distribution of Whistler Mode Waves in Jovian Inner Magnetosphere

AbstractWhistler mode waves are suggested to play a dual role in precipitation loss and acceleration of energetic electrons in Jovian magnetosphere. Using the combined wave data from Juno and Galileo, we constructed global maps of whistler mode waves in the Jovian inner magnetosphere (M‐shell <20). Whistler mode waves are found to be extensively present over M‐shells from 6 to ~13, peaking at ~10, and extend to magnetic latitudes at least up to 50°. Whistler mode wave intensities vary from a few pT to ~100 pT, similar to the intensity level at Earth. The new finding on the latitudinal extension of whistler mode waves indicates their potential effects on electron precipitation over a broad energy range from ~100 eV to several MeV. The newly constructed whistler mode wave spectra are crucial for evaluating the accurate role of whistler mode waves in energetic electron dynamics in the Jovian inner magnetosphere.