Shock Acceleration Research Articles

The Mechanism of Efficient Electron Acceleration at Parallel Nonrelativistic Shocks

Thermal electrons cannot directly participate in the process of diffusive acceleration at electron–ion shocks because their Larmor radii are smaller than the shock transition width: this is the well-known electron injection problem of diffusive shock acceleration. Instead, an efficient pre-acceleration process must exist that scatters electrons off of electromagnetic fluctuations on scales much shorter than the ion gyroradius. The recently found intermediate-scale instability provides a natural way to produce such fluctuations in parallel shocks. The instability drives comoving (with the upstream plasma) ion–cyclotron waves at the shock front and only operates when the drift speed is smaller than half of the electron Alfvén speed. Here we perform particle-in-cell simulations with the SHARP code to study the impact of this instability on electron acceleration at parallel nonrelativistic, electron–ion shocks. To this end, we compare a shock simulation in which the intermediate-scale instability is expected to grow to simulations where it is suppressed. In particular, the simulation with an Alfvénic Mach number large enough to quench the intermediate instability shows a great reduction (by two orders of magnitude) of the electron acceleration efficiency. Moreover, the simulation with a reduced ion-to-electron mass ratio (where the intermediate instability is also suppressed) not only artificially precludes electron acceleration but also results in erroneous electron and ion heating in the downstream and shock transition regions. This finding opens up a promising route for a plasma physical understanding of diffusive shock acceleration of electrons, which necessarily requires realistic mass ratios in simulations of collisionless electron–ion shocks.

Numerical Modeling of Spectral Hardening at a Finite-width Shock

Spectral hardening has been identified in solar flare hard X-ray observations for several decades and remains a puzzle. We examine spectral hardening under the diffusive shock acceleration mechanism using numerical simulations. The hardening is related to the finite width of the shock and is controlled by the shock Péclet number. We implement two different types of Monte Carlo simulations. The first is based on the backward stochastic differential equation method, where the Parker transport equation is solved by casting it to a set of stochastic different equations, and by following the trajectories of individual quasiparticles. In the second approach, we follow real particles and particles are assumed to move freely between scatterings from magnetic turbulence in the plasma. The scattering is modeled as either large-angle hard-sphere elastic collision, or small-angle pitch-angle scattering. We show that the results from these two approaches agree well with each other and agree with analytical results. We also use a Pan-spectrum form to fit the resulting spectra.

Testing the universality of cosmic-ray nuclei from protons to oxygen with AMS-02

The AMS-02 experiment has provided high-precision measurements of several cosmic-ray (CR) species. The achieved percent-level accuracy gives access to small spectral differences among the different species and, in turn, this allows scrutinizing the universality of CR acceleration, which is expected in the standard scenario of CR shock acceleration. While pre-AMS-02 data already indicated a violation of the universality between protons and helium, it is still an open question if at least helium and heavier nuclei can be reconciled. To address this issue, we performed a joint analysis using the AMS-02 CR measurements of antiprotons, protons, helium, helium 3, boron, carbon, nitrogen, and oxygen. We explore two competing propagation scenarios, one with a break in the diffusion coefficient at a few GVs and no reacceleration, and another one with reacceleration and with a break in the injection spectra of primaries. Furthermore, we explicitly consider the impact of the uncertainties in the nuclear production cross sections of secondaries by including nuisance parameters in the fit. The resulting parameter space is explored with the help of Monte Carlo methods. We find that, contrary to the naive expectation, in the standard propagation scenarios CR universality is violated also for He, on the one hand, and C, N, and O, on the other hand, i.e., different injection slopes (at the level of $\mathrm{\ensuremath{\Delta}}\ensuremath{\sim}0.05$) are required to explain the observed spectra. As an alternative, we explore further propagation scenarios, inspired by nonhomogeneous diffusion, which might save universality. Finally, we also investigate the universality of CR propagation, i.e., we compare the propagation properties inferred using only light nuclei ($\overline{p}$, p, He, $^{3}\mathrm{He}$) with the ones inferred using only heavier nuclei (B, C, N, O).

Modelling X-shaped radio galaxies: Dynamical and emission signatures from the Back-flow model

Context. Active galactic nuclei typically show the presence of radio jets ranging from sub-kiloparsec to megaparsec scales. Some of these radio galaxies show distortion in their jets, forming tailed or winged sources. X-shaped radio galaxies (XRGs) are a sub-class of winged sources, the formation mechanism of which is still unclear. Aims. The focus of this work is to understand hydro-dynamical back-flows and their role in dynamics and non-thermal emission signatures (in the presence of radiative losses and diffusive shock acceleration) during the initial phase of these galaxies. Methods. We performed relativistic magneto-hydrodynamic (RMHD) simulations of an under-dense jet travelling in a tri-axial ambient using a hybrid Eulerian-Lagrangian framework to incorporate effects of micro-physical processes. Results. We demonstrate the dominant role played by pressure gradient in shaping XRGs in thermally dominated cases. We show that the prominence of the formed structure decreases as the jet deviates from the major axis of the ambient. The wing evolution is mainly governed by re-energised particles due to shocks that keep the structure active during the evolution time. The synthetic intensity maps of the radio galaxy show similarities with morphologies that are typically found in observed XRGs. This includes the cases with wider wings than the active lobes. The characteristic emission signatures in terms of its synchrotron spectra and the implication of equipartition condition in age estimation are also discussed here. Additionally, we show that age discrepancies can be attributed to the mixing of different aged particle populations. Furthermore, the effect of the viewing angle on the difference of spectral index (Δα) of the active lobes and the wings shows a large variation and degenerate behaviour. We demonstrate the role of diffusive shocks in the obtained variation and conclude that the Δα spread is not a dependable characteristic in determining the formation model of XRGs.

Shocks and dust formation in nova V809 Cep

ABSTRACT The discovery that many classical novae produce detectable GeV γ-ray emission has raised the question of the role of shocks in nova eruptions. Here, we use radio observations of nova V809 Cep (nova Cep 2013) with the Jansky Very Large Array to show that it produced non-thermal emission indicative of particle acceleration in strong shocks for more than a month starting about 6 weeks into the eruption, quasi-simultaneous with the production of dust. Broadly speaking, the radio emission at late times – more than 6 months or so into the eruption – is consistent with thermal emission from $10^{-4}\, {\rm M}_\odot$ of freely expanding, 104 K ejecta. At 4.6 and 7.4 GHz, however, the radio light curves display an initial early-time peak 76 d after the discovery of the eruption in the optical (t0). The brightness temperature at 4.6 GHz on day 76 was greater than 105 K, an order of magnitude above what is expected for thermal emission. We argue that the brightness temperature is the result of synchrotron emission due to internal shocks within the ejecta. The evolution of the radio spectrum was consistent with synchrotron emission that peaked at high frequencies before low frequencies, suggesting that the synchrotron from the shock was initially subject to free–free absorption by optically thick ionized material in front of the shock. Dust formation began around day 37, and we suggest that internal shocks in the ejecta were established prior to dust formation and caused the nucleation of dust.

Detection of gamma-rays around SNR HB9 and its implications for the diffusive shock-acceleration history

Abstract We analyze the GeV gamma-ray emission data from the vicinity of the supernova remnant (SNR) HB9 (G160.9+2.6) from the Fermi-LAT 12 yr observations to quantify the evolution of diffusive shock acceleration (DSA) in the SNR. In the vicinity of HB9, there are molecular clouds whose locations do not coincide with the SNR shell in the line of sight. We detect significant gamma-ray emissions above 1 GeV spatially coinciding with the two prominent cloud regions, as well as emission from the SNR shell, the latter of which is consistent with the results of previous studies. The energy spectrum above 1 GeV in each region is fitted with a simple power-law function of dN/dE ∝ E−Γ. The fitting result indicates harder spectra, with power-law indices of Γ = 1.84 ± 0.18 and 1.84 ± 0.14, than that at the SNR shell, with Γ = 2.55 ± 0.10. The observed spectra from the cloud regions are found to be consistent with the theoretically expected gamma-ray emissions originating in the protons that escaped from SNR HB9, where particles can be accelerated up to higher energies than those in the shell at present. The resultant diffusion coefficient in the vicinity of the SNR is comparable to that of the Galactic mean.

NuSTAR discovery of the hard X-ray emission and a wide-band X-ray spectrum from the Pictor A western hotspot

Abstract Utilizing Chandra, XMM-Newton, and NuSTAR, a wide-band X-ray spectrum from 0.2 to 20 keV is reported from the western hotspot of Pictor A. In particular, the X-ray emission is significantly detected in the 3 to 20 keV band at 30σ by NuSTAR. This is the first detection of hard X-rays with energies above 10 keV from a jet termination hotspot of active galactic nuclei. The hard X-ray spectrum is well described with a power-law model with a photon index of Γ = 1.8 ± 0.2, and the flux is obtained to be (4.5 ± 0.4) × 10−13 erg s−1 cm−2 in the 3 to 20 keV band. The obtained spectrum is smoothly connected with those soft X-ray spectra observed by Chandra and XMM-Newton. The wide-band spectrum shows a single power-law spectrum with a photon index of Γ = 2.07 ± 0.03, excluding any cut-off/break features. Assuming the X-rays to be synchrotron radiation of the electrons, the energy index of the electrons is estimated as p = 2Γ − 1 = 3.14 ± 0.06 from the wide-band spectrum. Given that the X-ray synchrotron-emitting electrons quickly lose their initial energies via synchrotron radiation, the energy index of electrons at acceleration sites is estimated as pacc = p − 1 = 2.14 ± 0.06. This is consistent with the prediction of the diffusive shock acceleration. Since the spectrum has no cut-off feature up to 20 keV, the maximum electron energy is estimated to be no less than 40 TeV.

Investigating Superdiffusive Shock Acceleration at a Parallel Shock with a Fractional Parker Equation for Energetic-particle Interaction with Small-scale Magnetic Flux Ropes

It has been suggested before that small-scale magnetic flux rope (SMFR) structures in the solar wind can temporarily trap energetic charged particles. We present the derivation of a new fractional Parker equation for energetic-particle interaction with SMFRs from our pitch-angle-dependent fractional diffusion-advection equation that can account for such trapping effects. The latter was derived previously in le Roux & Zank from the first principles starting with the standard focused transport equation. The new equation features anomalous advection and diffusion terms. It suggests that energetic-particle parallel transport occurs with a decaying efficiency of advection effects as parallel superdiffusion becomes more dominant at late times. Parallel superdiffusion can be linked back to underlying anomalous pitch-angle transport, which might be subdiffusive during interaction with quasi-helical coherent SMFRs. We apply the new equation to time-dependent superdiffusive shock acceleration at a parallel shock. The results show that the superdiffusive-shock-acceleration timescale is fractional, the net fractional differential particle flux is conserved across the shock ignoring particle injection at the shock, and the accelerated particle spectrum at the shock converges to the familiar power-law spectrum predicted by standard steady-state diffusive-shock-acceleration theory at late times. Upstream, as parallel superdiffusion progressively dominates the advection of energetic particles, their spatial distributions decay on spatial scales that grow with time. Furthermore, superdiffusive parallel shock acceleration is found to be less efficient if parallel anomalous diffusion is more superdiffusive, while perpendicular particle escape from the shock, thought to be subdiffusive during SMFR interaction, is reduced when increasingly subdiffusive.

Collision of an acceleration wave with blast wave in van der Waals dusty reacting gases

A system of hyperbolic partial differential equations describing a one-dimensional planar and radially symmetric flow of real dusty reacting gases is considered. The transport equation for an acceleration wave is obtained to analyze the evolution of the acceleration wave via a particular solution for the system under consideration. The Rankine–Hugoniot jump conditions across the blast wave are used to determine Lax entropy conditions for a physical blast wave. Furthermore, amplitudes of reflected waves, transmitted waves, and the bounce in shock acceleration, which arises from the collision between an acceleration wave and a blast wave, are determined.

Microphysics of Diffusive Shock Acceleration: Impact on the Spectrum of Accelerated Particles

Diffusive shock acceleration at collisionless shocks remains the most likely process for accelerating particles in a variety of astrophysical sources. While the standard prediction for strong shocks is that the spectrum of accelerated particles is universal, f(p) ∝ p −4, numerous phenomena affect this simple conclusion. In general, the nonlinear dynamical reaction of accelerated particles leads to a concave spectrum, steeper than p −4 at momenta below a few tens of GeV c −1 and harder than the standard prediction at high energies. However, the nonlinear effects become important in the presence of magnetic field amplification, which in turn leads to higher values of the maximum momentum p max. It was recently discovered that the self-generated perturbations that enhance particle scattering, when advected downstream, move in the same direction as the background plasma, so that the effective compression factor at the shock decreases and the spectrum becomes steeper. We investigate the implications of the excitation of the non-resonant streaming instability on these spectral deformations, the dependence of the spectral steepening on the shock velocity, and the role played by the injection momentum.

Generation of polarized proton beams with gaseous targets from CO2-laser-driven collisionless shock acceleration

We propose obtaining polarized proton beams based on CO2-laser-driven collisionless shock acceleration (CSA) of the pre-polarized HCl gas. By tailoring the density profile of the pre-polarized HCl gas, the intense CO2 laser pulse heats the plasma target and forms a strong shock that reflects the polarized protons to high energy. According to particle-in-cell simulations implemented with the spin dynamics, directional proton beams of several MeV were generated at a total beam polarization of over 80%. Simulations showed that proton spin precession occurred in the azimuthal magnetic fields generated by the Biermann effect and plasma currents. The latter was the main depolarization mechanism in the early stage of shock wave formation. For CSA at CO2 laser intensities around 1017–1018 W/cm2, the proton depolarization was insignificant and the beam polarization purity was preserved. As pre-polarized hydrogen targets were available at gaseous densities in-state-of-art facilities, CSA driven by relatively long wavelength lasers provided a feasible solution for obtaining ultra-fast polarized proton sources.

Flare echoes from relaxation shocks in perturbed relativistic jets

Context. One of the main scenarios to account for the multiwavelength flux variability observed in relativistic jets of active galactic nuclei (AGNs) is based on the diffusive shock acceleration of a population of relativistic electrons on internal shocks of various origins. Any complete AGN emission scenario has to be able to explain the wide range of observed variability timescales, which change over several orders of magnitude between the radio and gamma-ray band. In addition to observations of flux variability, constraints are also provided by very-long-baseline interferometry (VLBI), which shows a large variety of moving and standing emission zones with distinct behaviors. Aims. Combining dynamic hydrodynamic jet simulations with radiative transfer, we aim to characterize the evolution of stationary and moving emission zones in the jet and study their multiwavelength signatures through emission maps and light curves. We focus our study on flare events that occur during strong interactions between moving ejecta and stationary recollimation shocks. Such events are shown to lead to a significant perturbation of the stationary jet structure. Methods. We simulate relativistic jets with the magneto-hydrodynamic code MPI-AMRVAC and inject nonthermal particle distributions of electrons into shock regions. We follow the propagation of a moving shock and its interactions with a structure of standing recollimation shocks in the jet. Synchrotron emission and radiative transfer are calculated in the post-processing code RIPTIDE for given observation angles and frequencies, assuming a turbulent magnetic field and taking the light crossing effect into account. Results. In the case of strong shock–shock interactions, we demonstrate the appearance of trailing components behind the leading moving shock. The latter destabilizes the jet, causing the emergence of oscillating standing shocks and relaxation shocks. Emissions from these regions can dominate the overall flux or lead to “flare echoes” in the light curve. Another observational marker for the presence of relaxation shocks appears in time-distance plots of bright VLBI components of the jet. Our scenario provides a plausible explanation for radio VLBI observations of the radio galaxy 3C 111, where trailing components were observed during a radio outburst event in 1997, and may be applicable to other sources with similar features.

Electron Acceleration by Moderate-Mach-number Low-β Shocks: Particle-in-Cell Simulations

Particle acceleration is ubiquitous at shock waves, occurring on scales ranging from supernova remnants in the universe to coronal-mass-ejection-driven shocks and planetary bow shocks in the heliosphere. The most promising mechanism responsible for the almost universally observed power-law spectra is diffusive shock acceleration (DSA). However, how electrons are preaccelerated by different shocks to the energy required by the DSA theory is still unclear. In this paper, we perform two-dimensional particle-in-cell plasma simulations to investigate how the magnetic field orientations, with respect to simulation planes, affect electron preacceleration in moderate-Mach-number low- β shocks. Simulation results show that instabilities can be different as the simulation planes capture different trajectories of particles. For magnetic fields perpendicular to the simulation plane, electron cyclotron drift instability dominates in the foot. Electrons can be trapped by the electrostatic wave and undergo shock-surfing acceleration. For magnetic fields lying in the simulation plane, whistler waves produced by modified two-stream instability dominate in the foot and scatter the electrons. In both cases, electrons undergo multistage acceleration in the foot, shock surface, and immediate downstream, during which process shock-surfing acceleration takes place as part of the preacceleration mechanism in moderate-Mach-number quasi-perpendicular shocks.

Spectral softening in core-collapse supernova remnant expanding inside wind-blown bubble

Context. Galactic cosmic rays (CRs) are widely assumed to arise from diffusive shock acceleration, specifically at shocks in supernova remnants (SNRs). These shocks expand in a complex environment, particularly in the core-collapse scenario as these SNRs evolve inside the wind-blown bubbles created by their progenitor stars. The CRs at core-collapse SNRs may carry spectral signatures of that complexity. Aims. We study particle acceleration in the core-collapse SNR of a progenitor with an initial mass of 60 M⊙ and realistic stellar evolution. The SNR shock interacts with discontinuities inside the wind-blown bubble and generates several transmitted and reflected shocks. We analyse their impact on particle spectra and the resulting emission from the remnant. Methods. To model the particle acceleration at the forward shock of a SNR expanding inside a wind bubble, we initially simulated the evolution of the pre-supernova circumstellar medium (CSM) by solving the hydrodynamic equations for the entire lifetime of the progenitor star. As the large-scale magnetic field, we considered parameterised circumstellar magnetic field with passive field transport. We then solved the hydrodynamic equations for the evolution of a SNR inside the pre-supernova CSM simultaneously with the transport equation for CRs in test-particle approximation and with the induction equation for the magnetohydrodynamics in 1D spherical symmetry. Results. The evolution of a core-collapse SNR inside a complex wind-blown bubble modifies the spectra of both the particles and their emission on account of several factors including density fluctuations, temperature variations, and the magnetic field configuration. We find softer particle spectra with spectral indices close to 2.5 during shock propagation inside the shocked wind, and this softness persists at later evolutionary stages. Further, our calculated total production spectrum released into the interstellar medium demonstrates spectral consistency at high energy (HE) with the injection spectrum of Galactic CRs, which is required in propagation models. The magnetic field structure effectively influences the emission morphology of SNRs as it governs the transportation of particles and the synchrotron emissivity. There is rarely a full correspondence of the intensity morphology in the radio, X-ray, and gamma-ray bands.

A Perspective on Solar Energetic Particles

The author has been fortunate to observe and participate in the rise of the field of solar energetic particles (SEPs), from the early abundance studies, to the contemporary paradigm of shock acceleration in large SEP events, and element abundance enhancements that are power laws in mass-to-charge ratios from H to Pb. Through painful evolution the “birdcage” model and the “solar-flare myth” came and went, leaving us with shock waves and solar jets that can interact as sources of SEPs.

Kinetic simulation of electron, proton and helium acceleration in a non-relativistic quasi-parallel shock

ABSTRACT In addition to accelerating electrons and protons, non-relativistic quasi-parallel shocks are expected to possess the ability to accelerate heavy ions. The shocks in supernova remnants are generally supposed to be accelerators of Galactic cosmic rays, which consist of many species of particles. We investigate the diffusive shock acceleration of electrons, protons and helium ions in a non-relativistic quasi-parallel shock through a 1D particle-in-cell simulation with a helium-to-proton number density ratio of 0.1, which is relevant for Galactic cosmic rays. The simulation indicates that waves can be excited by the flow of energetic protons and helium ions upstream of a non-relativistic quasi-parallel shock with a sonic Mach number of 14 and an Alfvén Mach number of 19.5 in the shock rest frame, and that the charged particles are scattered by the self-generated waves and accelerated gradually. Moreover, the spectra of the charged particles downstream of the shock are thermal with a non-thermal tail, and the acceleration is efficient, with about $7{{\ \rm per\ cent}}$ and $5.4{{\ \rm per\ cent}}$ of the bulk kinetic energy transferred into the non-thermal protons and helium ions, respectively, in the near downstream region by the end of the simulation.

Transport Vibration and Shock Characteristics of A 110 kV/40MVA Vehicular Mobile Transformer

Vehicular mobile transformers will suffer from frequent vibration and shock during transportation, which may lead to the damage of transformers. In order to understand the characteristics of vibration and shock during transportation, the three‐axis vibration and shock acceleration of a 110 kV/40MVA vehicular mobile transformer was measured by using a self‐developed transportation condition monitoring system. The time‐domain characteristics and frequency‐domain characteristics were analyzed. The relationship of vibration and shock acceleration with driving speed was also discussed. Results show that the y‐axis vibration and shock acceleration is generally the lowest. The main frequency of x‐axis acceleration is 4–8 Hz, while y‐axis acceleration is 1–7 Hz and 25–28 Hz, and z‐axis acceleration is 1–5 Hz. The related scattered points of the vibration acceleration with the driving speed are approximately distributed on a straight line, and that of the shock acceleration with the driving speed are approximately distributed on an exponential function curve. According to the limitation of 3 g vibration and shock acceleration in international standards, the driving speed of the 110 kV vehicular mobile transformer in highway, highway ramp and the first class road are suggested to be limited to 66, 51, and 49 km/h, respectively. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Diffusive Shock Acceleration at Oblique High Mach Number Shocks

Abstract The current paradigm of cosmic-ray (CR) origin states that the greater part of galactic CRs is produced by supernova remnants. The interaction of supernova ejecta with the interstellar medium after a supernova's explosions results in shocks responsible for CR acceleration via diffusive shock acceleration (DSA). We use particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique to investigate whether DSA can occur in oblique high Mach number shocks. Using the PIC method, we follow the formation of the shock and determine the fraction of the particles that gets involved in DSA. With this result, we use PIC-MHD simulations to model the large-scale structure of the plasma and the magnetic field surrounding the shock and find out whether or not the reflected particles can generate upstream turbulence and trigger DSA. We find that the feasibility of this process in oblique shocks depends strongly on the Alfvénic Mach number, and the DSA process is more likely to be triggered at high Mach number shocks.

Herscheldiscovery of far-infrared emission from the hotspot D in the radio galaxy Cygnus A

ABSTRACTThe far-infrared counterpart of hotspot D, the terminal hotspot of the eastern jet hosted by the radio galaxy Cygnus A, is detected with Herschel Aperture photometry of the source performed in 5 photometric bands covering the wavelength range of 70–350 $\mu$m. After removing the contamination from another nearby hotspot, E, the far-infrared intensity of hotspot D is derived as 83 ± 13 and 269 ± 66 mJy at 160 and 350 $\mu$m, respectively. Since the far-infrared spectrum of the object smoothly connects to the radio one, the far-infrared emission is attributed to the synchrotron radiation from the radio-emitting electron population. The radio-to-near-infrared spectrum is confirmed to exhibit a far-infrared break feature at the frequency of $\nu _\mathrm{br}=2.0^{+1.2}_{-0.8} \times 10^{12}$ Hz. The change in energy index at the break (Δα = 0.5) is interpreted as the impact of radiative cooling on an electron distribution sustained by continuous injection from diffusive shock acceleration. By ascribing the derived break to this cooling break, the magnetic field, B, in the hotspot is determined as a function of its radius, R within a uniform one-zone model combined with the strong relativistic shock condition. An independent B–R constraint is obtained by assuming the X-ray spectrum is wholly due to synchrotron self-Compton emission. By combining these conditions, the two parameters are tightly determined as B = 120–150 μG and R = 1.3–1.6 kpc. A further investigation into the two conditions indicates the observed X-ray flux is highly dominated by the synchrotron self-Compton emission.

Energy Spectra vs. Element Abundances in Solar Energetic Particles and the Roles of Magnetic Reconnection and Shock Acceleration

We reexamine the relationship between energy spectral indices and element abundance enhancements in solar energetic particle (SEP) events at energies of a few MeV amu−1. We find a correlated behavior only in the largest gradual SEP4 events when all ions are accelerated from the ambient coronal plasma by shock waves driven by fast, wide coronal mass ejections (CMEs). This correlated abundance behavior can track complex time variations in the spectral indices during an event. In other (SEP3) events, CME-driven shock waves, days apart, sample seed particles from a single pool of suprathermal impulsive ions contributed earlier. Of the smaller, Fe-rich, impulsive SEP events, previously related to magnetic reconnection in solar jets, over half are subsequently reaccelerated by CME-driven shock waves (SEP2), causing typical ion intensities to have a 64% correlation with shock speeds. In these SEP2 events, the onset of shock acceleration is signaled by a new component in the abundances, large proton excesses. The remaining SEP1 events lack evidence of shock acceleration. However, for all these events (SEP1–SEP3) with abundances determined by magnetic reconnection, energy spectra and abundances are decoupled.