Strong Particle Acceleration Research Articles

Investigation of a Magnetic Reconnection Event with Extraordinarily High Particle Energization in Magnetotail Turbulence

Magnetic reconnection and plasma turbulence are ubiquitous and key processes in the Universe. These two processes are suggested to be intrinsically related: magnetic reconnection can develop turbulence, and, in turn, turbulence can influence or excite magnetic reconnection. In this study, we report a rare and unique electron diffusion region (EDR) observed by the Magnetospheric Multiscale mission in the Earth’s magnetotail with significantly enhanced energetic particle fluxes. The EDR is in a region of strong turbulence within which the plasma density is dramatically depleted. We present three salient features. (1) Despite the turbulence, the EDR behaves nearly the same as that in 2D quasi-planar reconnection; the observations suggest that magnetic reconnection continues for several minutes. (2) The observed reconnection electric field and inferred energy transport are exceptionally large. However, the aspect ratio of the EDR (one definition of reconnection rate) is fairly typical. Instead, extraordinarily large-amplitude Hall electric fields appear to enable the strong energy transport. (3) We hypothesize that the high-energy transport rate, density depletion, and the strong particle acceleration are related to a near-runaway effect, which is due to the combination of low-plasma-density inflow (from lobes) and possible positive feedback between turbulence and reconnection. The detailed study on this EDR gives insight into the interplay between reconnection and turbulence, and the possible near-runaway effect, which may play an important role in other particle acceleration in astrophysical plasma.

Evolvement of microwave spike bursts in a solar flare on 2006 December 13

Solar radio spikes are one of the most intriguing spectral types of radio bursts. Their very short lifetimes, small source size and super-high brightness temperature indicate that they should be involved in some strong energy release, particle acceleration and coherent emission processes closely related to solar flares. In particular, for the microwave spike bursts, their source regions are much close to the related flaring source region which may provide the fundamental information of the flaring process. In this work, we identify more than 600 millisecond microwave spikes which recorded by the Solar Broadband Radio Spectrometer in Huairou (SBRS/Huairou) during an X3.4 solar flare on 2006 December 13 and present a statistical analysis about their parametric evolution characteristic. We find that the spikes have nearly the same probability of positive and negative frequency drifting rates not only in the flare rising phase, but also in the peak and decay phases. So we suppose that the microwave spike bursts should be generated by shock-accelerated energetic electrons, just like the terminational shock (TS) wave produced by the reconnection outflows near the loop top. The spike bursts occurred around the peak phase have the highest central frequency and obviously weak emission intensity, which imply that their source region should have the lowest position with higher plasma density due to the weakened magnetic reconnection and the relaxation of TS during the peak phase. The right-handed polarization of the most spike bursts may be due to the TS lying on the top region of some very asymmetrical flare loops.

On the requirement for a high resolution spectrograph to investigate the multiplicity of massive stars with the 3.6-m Devasthal Optical Telescope

The investigation of the multiplicity of massive stars constitutes a key aspect of their understanding. On the one hand, the evolution of short period systems can be tremendously influenced by the companion, for instance through mass exchange or common envelope evolution. On the other hand, the wind-wind interaction region in massive multiple systems is the seat of a high level physics, including strong thermal X-ray emission, particle acceleration and non-thermal emission processes. The description and understanding of these processes require the accurate determination of orbital parameters, notably through spectroscopic studies. In this context, it is timely to anticipate some relevant applications of a high resolution spectrograph (HRS) to be mounted on the Devasthal Optical Telescope, emphasizing its potential complementarity with other Indian facilities such as the GMRT and Astrosat.

“Diffusion” region of magnetic reconnection: electron orbits and the phase space mixing

Abstract. The nonlinear dynamics of electrons in the vicinity of magnetic field neutral lines during magnetic reconnection, deep inside the “diffusion” region where the electron motion is nonadiabatic, has been numerically analyzed. Test particle orbits are examined in that vicinity, for a prescribed planar two-dimensional magnetic field configuration and with a prescribed uniform electric field in the neutral line direction. On electron orbits, a strong particle acceleration occurs due to the reconnection electric field. Local instability of orbits in the neighborhood of the neutral line is pointed out. It combines with finiteness of orbits due to particle trapping by the magnetic field, and this should lead to the effect of mixing in the phase space, and the appearance of dynamical chaos. The latter may presumably be viewed as a mechanism producing finite “conductivity” in collisionless plasma near the neutral line. That conductivity is necessary to provide violation of the magnetic field frozen-in condition, i.e., for magnetic reconnection to occur in that region. Keywords. Magnetospheric physics (plasma sheet)

Sandpile Models and Solar Flares: Eigenfunction Decomposition for Data Assimilation

AbstractThe largest solar flares, of class X and above, are often associated with strong energetic particle acceleration. Based on the self-similar distribution of solar flares, self-organized criticality models such as sandpiles can be used to successfully reproduce their statistics. However, predicting strong (and rare) solar flares turns out to be a significant challenge. We build here on an original idea based on the combination of minimalistic flare models (sandpiles) and modern data assimilation techniques (4DVar) to predict large solar flares. We discuss how to represent a sandpile model over a reduced set of eigenfunctions to improve the efficiency of the data assimilation technique. This improvement is model-independent and continues to pave the way towards efficient near real-time solutions for predicting solar flares.

Properties of hot electrons in the Jovian inner magnetosphere deduced from extended observations of the Io Plasma Torus

AbstractOne of the focal points of interest in Jovian magnetospheric physics is the transport of energy and particles into the inner region. While an explosive energy release event in the midmagnetosphere is manifested as an aurora transient, its connection to the inner part has not been investigated due to sparsity of observations. Here we take the advantage of long‐term and quasi‐continuous simultaneous monitoring of the polar aurora and the Io Plasma Torus (IPT) located in the inner magnetosphere by Extreme Ultraviolet Spectroscope for Exospheric Dynamics/Hisaki. Studies on temporal characteristics over hours enable us to see slow (~10 h) coupling between the middle and inner magnetosphere as well as to quantify the temperature of hot electrons in the IPT. We derive parameters that characterize the strong particle acceleration process.

Angular momentum transport and particle acceleration during magnetorotational instability in a kinetic accretion disk.

Angular momentum transport and particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk are investigated using three-dimensional particle-in-cell simulation. We show that the kinetic MRI can provide not only high-energy particle acceleration but also enhancement of angular momentum transport. We find that the plasma pressure anisotropy inside the channel flow with p(∥)>p(⊥) induced by active magnetic reconnection suppresses the onset of subsequent reconnection, which, in turn, leads to high-magnetic-field saturation and enhancement of the Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection, the plasma isotropization progresses in the channel flow and the anisotropic plasma with p(⊥)>p(∥) due to the dynamo action of MRI outside the channel flow contribute to rapid reconnection and strong particle acceleration. This efficient particle acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high-energy particles observed around massive black holes.

The effect of parallel electric field in shock waves on the acceleration of relativistic ions, electrons, and positrons

The effect of an electric field E∥ parallel to the magnetic field B on particle acceleration in shock waves is studied. With test particle calculations, for which the electromagnetic fields of shock waves are obtained from one-dimensional, fully kinetic, electromagnetic, particle simulations, the motions of relativistic ions, electrons, and positrons are analyzed. In these simulations, the shock speed vsh is taken to be close to c cos θ, where θ is the angle between the external magnetic field and wave normal, and thus strong particle acceleration takes place. Test particle motions calculated in two different methods are compared: In the first method the total electric field E is used in the equation of motion, while in the second method E∥ is omitted. The comparison confirms that in the acceleration of relativistic ions E∥ is unimportant for high-energy particles. For the acceleration of electrons and positrons, however, E∥ is essential.

On the plasma temperature in supernova remnants with cosmic-ray modified shocks

Context: Multiwavelength observations of supernova remnants can be explained within the framework of the diffusive shock acceleration theory, which allows effective conversion of the explosion energy into cosmic rays. Although the models of nonlinear shocks describe reasonably well the nonthermal component of emission, certain issues, including the heating of the thermal plasma and the related X-ray emission, remain still open. Aims: To discuss how the evolution and structure of supernova remnants is affected by strong particle acceleration at the forward shock. Methods: Analytical estimates combined with detailed discussion of the physical processes. Results: The overall dynamics is shown to be relatively insensitive to the amount of particle acceleration, but the post-shock gas temperature can be reduced to a relatively small multiple, even as small as six times, the ambient temperature with a very weak dependence on the shock speed. This is in marked contrast to pure gas models where the temperature is insensitive to the ambient temperature and is determined by the square of the shock speed. It thus appears to be possible to suppress effectively thermal X-ray emission from remnants by strong particle acceleration. This might provide a clue for understanding the lack of thermal X-rays from the TeV bright supernova remnant RX J1713.7-3946.

Controlled plasma wave generation and particle acceleration through seeding of the forward Raman scattering instability

Trapping and acceleration of background plasma electrons in plasma waves generated by low energy (<0.1J) laser pulses copropagating with much weaker (1% in intensity) seed pulses that are down shifted in frequency by ωp is investigated in the self-modulation regime by one-dimensional (1D) and 2D particle-in-cell simulations. Without the seed, the modulation for pulses of subcritical power is found to develop slowly compared to the interaction time limited by diffraction and dephasing. With the seed, on the other hand, strong primary pulse modulation, wakefield excitation, and particle trapping and acceleration can be achieved reproducibly. Moreover, in contrast to incoherent seeding mechanisms such as ionization, the seed pulse enables coherent control of the excited wakefield. The simulations show that 38 mJ seeded pulses can generate relativistic bunches of ∼0.5nC. Seeded acceleration by pulses of subcritical power (P=1∕2Pc, or 19 mJ) is demonstrated by simulations in a performed plasma channel

Circulation of ionospheric and solar wind particle populations during extended southward interplanetary magnetic field

Single particles trajectories using time‐dependent electric and magnetic fields from multifluid simulations are used to examine the energy and mass transport due to entry of solar wind particles and from ionospheric outflows incorporating both light and heavy ions. It is shown the particles move with the convection cells derived from the multifluid simulations, and that strong particle acceleration occurs at both the dayside and nightside tips of the flow reversal regions. However, different particle populations have limited access to various parts of the convection pattern, and this leads to substantial dawn‐dusk asymmetries in the particle populations within the magnetosphere. For the strong southward interplanetary magnetic field (IMF) conditions for the event studied, fast solar wind particles are able to enter from the dawnside and contribute to the asymmetric ring current. The rest of the fast particles flow down the mantle and do not enter the near‐Earth magnetosphere. The remaining slow component is convected into the magnetosphere over a few tens of minutes to form cold populations in the mantle and LLBL. Solar wind He++ and O6+ are shown to penetrate deeper than the solar wind protons. Light ionospheric ions from the cusp and dawnside auroral oval have similar access problems and flow primarily down the tail and make little contribution to the plasma content to the near‐Earth plasma sheet. Nightside auroral protons are shown to form a cold component in the plasma sheet boundary layer. When they are eventually convected in to the near‐Earth plasma sheet they are accelerated preferentially to the duskside and experience further energy gains as they are convected sunward. These energetic protons contribute to the asymmetric ring current, with leakage from the magnetosphere occurring as they approach the dayside reconnection region. Heavy ionospheric ions enter the convection pattern differently from their light ions counterparts. O+ ions from the cusp can enter the near‐Earth plasma sheet to provide some mass loading, but the biggest contributor is the dawnside auroral oval. The dawn‐dusk electric field accelerates these ions toward the dusk side, but on sufficient low L shells that these ions can dominate the symmetric ring current composition. The O+ ions that originate from the midnight and dusk sectors go to forming hot populations in the dusk LLBL.

Hard X-rays from Slow Flares

“Slow LDEs” are those for which the rise phase is slow, as well as the decay phase. Such flares follow the Neupert effect, which implies that the non-thermal energy release has a similar relationship to heating as in a normal impulsive flare. Based on a sample of 53 slow LDEs during the first nine years of Yohkoh observations, we find 19 for which substantial overlap occurs with BATSE hard X-ray observations. These events tend strongly to have extended hard X-ray emission even though their hard X-ray emission does not tend to be “impulsive” in the sense of rapid variation. The hard X-ray fluences for these 19 events correlate with the soft X-ray peak fluxes, implying strong non-thermal particle acceleration even for these relatively slow energy-release rates. These events often correspond to the occurrence of “supra-arcade downflows,” a phenomenon consistent with the classical reconnection model for gradual-phase flare energy release. This correspondence suggests a close relationship, not depending strongly upon time scale, between large-scale reconnection and the acceleration of non-thermal electrons.

Test particle acceleration in 2D current sheets undergoing dynamical phases of reconnection

Calculations of collision-free test particle orbits in a dynamic, filamentary current sheet are presented. The electromagnetic fields are obtained from a two-dimensional MHD simulation; thus this study is restricted to energization in perpendicular electric fields. Starting from a multiple X-line initial perturbation, the current sheet undergoes complex dynamics, comprising a tearing-like phase, multiple island coalescence and plasmoid formation, and finally the acceleration and ejection of the plasmoid. The dynamic, multiple X-line configuration possesses two important properties supporting strong particle acceleration: efficient particle confinement which permits multiple or long-lasting acceleration phases, and appropriate asymmetries of the average electric field about the O-lines, which permits acceleration of the majority of test particles. Dynamic current sheets may thus be responsible for the efficient bulk acceleration of particles observed in the impulsive phase of solar flares. For parameters of the lower solar corona, sub-second acceleration times and maximum energies in the 10 7–10 8 eV range are obtained.

Signatures for remote sensing of reconnection in the distant magnetotail

Satellite observations have revealed that ionospheric and solar wind plasmas are essentially energized inside the Earth's magnetosphere and especially in the magnetotail. Current sheet acceleration and reconnection were proposed to be the main energization processes. Unfortunately, traditional measurement techniques did not allow decisive conclusions about the actually acting processes, their sites and main parameters. Meanwhile, higher resolution measurements have been obtained from GEOTAIL and multi-point observations will be available soon from INTERBALL and CLUSTER. Hence, appropriate analysis methods are needed to deduce the information contained in high-resolution measurements. Indeed, theoretical predictions have been derived recently of structures in the ion distribution due to current sheet acceleration. Our quasi-adiabatic theory of acceleration in one-dimensional and weakly two-dimensional current sheets allowed to understand the formation of these structures and to predict their scaling laws. This theory was, however, not applicable to the case of strong acceleration by reconnection. Currently we have developed a new quasi-adiabatic theory of strong particle acceleration in essentially two-dimensional reconnection fields. As a result we have predicted the formation of structures in the spectrum of ions, accelerated by reconnection. These structures are different from those, predicted earlier for current sheet acceleration. In order to verify our new predictions we have carried out test particle calculations. Some of their results are presented here in this paper.

Nonlinear effects of the magnetotail particle motion in time-dependent electric field

The Motion of charged particle in magnetotail-like reversal field with time dependent electric field is studied analytically and numerically using a test particle approach. Variations in the solar wind magnetic and/or velocity can induce a time-dependent electric field in the magnetotail. Interaction of the magnetotail particles with this electric field can give rise to stochasticity. Energy coupling from the field to the plasma is due to stochastic motion of the particles and is termed “stochastic heating” or “stochastic acceleration”. The stochasticity can lead to heating of the plasma and to strong particle acceleration. The process can provide an explanation to the difference between ion and electron temperatures in the plasma sheet.

A detailed study of sheared Alfven waves and their possible application to gamma-ray bursts

view Abstract Citations (6) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Detailed Study of Sheared Alfven Waves and Their Possible Application to Gamma-Ray Bursts Fatuzzo, Marco ; Melia, Fulvio Abstract Strong particle acceleration in neutron-star environments may result in the upscattering of soft photons to gamma-ray energies. Sheared Alfven waves, which may be generated by several plausible disturbances in the stellar crust, can energize the charges to Lorentz factors in excess of 10 exp 5. However, a full understanding of the physics of these MHD waves is lacking due to the complications arising from the charge separation within the sheared region. Here, we present a detailed study of this mechanism, with particular attention to a comparison of the nonrelativistic and relativistic domains. We find that the charge separation is consistent with our previous classical MHD solutions and that it provides a natural description of the sheared current via a relativistic flow. These waves can apparently produce the particle distributions that are necessary to produce the gamma-ray fluxes observed in gamma-ray bursts, regardless of whether the sources are Galactic or extragalactic. Publication: The Astrophysical Journal Pub Date: April 1993 DOI: 10.1086/172549 Bibcode: 1993ApJ...407..680F Keywords: Gamma Ray Bursts; Neutron Stars; Plasma Waves; Computational Astrophysics; Particle Acceleration; Plasma Dynamics; Shear; Astrophysics; GAMMA RAYS: BURSTS; ACCELERATION OF PARTICLES; MAGNETOHYDRODYNAMICS: MHD; STARS: NEUTRON full text sources ADS |

Flare onsets in hard and soft X-rays

We show that the onset of solar flares, within ⩽ 2 minutes before the impulsive peaks, is characterized by an increase in high energy emission at E < 100 keV, and strong broadening of soft X-ray lines characteristic of the 10 7 K plasma already present at this stage. The observations are interpreted in terms of the early signature of energy release, during a phase preceding the instability that leads to strong particle acceleration.