摘要:

We review the evidence for the acceleration of charged particles to relativistic energies associated with solar flares from 1942, the time of their discovery, to the present. First, we present a brief summary of early attempts to identify the mechanism which accelerates the charged particles in solar flares. Second, we describe observational progress made before 1970 which revealed additional properties of the solar flare particle acceleration process. Also, some relevant, significant pre‐1970 theoretical advances are mentioned. Third, the neutral high‐energy observational data, obtained since 1972, are reviewed as diagnostics for the properties of the accelerated electrons and ions. These provide constraints for acceleration theories. Finally, the capabilities of stochastic, direct electric field, and shock acceleration mechanisms are briefly discussed. The early concept that the particles are accelerated in a two‐phase process in which electrons are first accelerated to ∼100 keV, followed by a longer term process which accelerates ions to relativistic energies is not consistent with observations. Rather, ions and electrons are accelerated together and the basic acceleration mechanisms, i.e., stochastic, direct electric field, and shock acceleration may all be operative in a flare. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50997

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We review the recent evidence that distinguishes particles accelerated in flares and in shock waves driven by coronal mass ejections (CMEs). CME‐driven shocks, not flares, produce most of the large particle events at 1 AU and can accelerate protons up to 20 GeV. In contrast, flare‐accelerated ions have characteristic abundances produced by resonant wave‐particle interactions in the flare plasma. Only the direct particle observations have allowed us to study this new physics of ion acceleration in flares, since the energetic ion abundances have been largely invisible in photons. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50970

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We expand Reames’ tabular summary of the two‐class picture of solar energetic particle (SEP) events to include characteristics of the particles that interact at the Sun to produce gamma‐ray emission. This addition underscores the contributions of gamma‐ray observations to our current understanding. The broad picture that is emerging is remarkable for its simplicity: while SEP events come in two basic types depending on the duration of the associated flare, the interacting particles in impulsive and gradual flares appear to be indistinguishable and resemble the SEPs observed in space following impulsive flares. The expanded classification system includes hybrid events, i.e., flares in which the gradual/impulsive distinction is blurred and for which the SEP events contain a mixture of flare‐accelerated and CME/shock‐accelerated particles. We argue that SEP events associated with long duration flares can be expected to have a temporally and spatially confined ‘‘core’’ of flare‐accelerated particles surrounded by a ‘‘halo’’ of CME/shock particles. Thus SEP composition should be checked in comparative studies of gamma‐ray emission and particles in space to ensure that the SEPs are flare‐accelerated. We discuss how recently‐discovered types of gamma‐ray flares (electron‐dominated events, spatially and temporally extended gamma‐ray events) may fit into the expanded classification scheme. We suggest that the acceleration process in the pion‐rich phase of large flares (e.g., 1982 June 3) is similar to that occurring earlier in the flare, the main differences being the greater height of the acceleration region and the presence of previously accelerated seed particles. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50980

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We review the observations relating solar energetic particle (SEP) events to coronal mass ejections (CMEs). Nearly every gradual SEP event is associated with a fast (v≳400 km/s) CME, which is presumed to drive a coronal shock that accelerates the SEPs. Evidence supporting the contention that all SEP ions observed in large, gradual events are shock accelerated is reviewed. Evidence for shock acceleration of electrons is found to be more ambiguous. The following current questions in SEP/CME relationships are discussed: 1. SEP production by electric fields in post‐flare loops; 2. the relationship of type II burst shocks and CME‐driven shocks; 3. flare impulsive phase contributions to SEP events; and 4. the evidence for shock‐accelerated (SA) events; and 5. progressively hardening X‐ray spectra and SEP events. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50989

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We analyze solar energetic electron events measured with particle detectors on board of theISEE‐3 (ICE) andHelios1 and 2 spacecraft. Energy spectra in the range 0.1 to tens of MeV are generated applying the results of a careful re‐examination of the electron response function of the instruments. The spectral shapes of events observed simultaneously, among them five on all threes/c, are in very good agreement inspite of the sometimes considerable difference in azimuthal and radial distances of thes/cwith respect to the flare. These findings suggest that transport processes at the Sun and in the interplanetary medium depend only weakly on the electron energy and that the observed spectra are representative of the accelerated electron spectra at the Sun. A comparison of the electron spectra with SMM gamma‐ray spectra gives evidence for the existence of different acceleration and emission mechanism in flares with long (LDEs) and short duration (SDEs) soft X‐ray emission. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50990

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The mean charge states of abundant heavy ions with ∼15–70 MeV nucleon−1in the two large solar energetic particle events of 1992 October 30 and November 2 have been determined using measurements of the invariant latitude of the cosmic ray geomagnetic cutoffs as a function of time, particle energy, and element from the Mass Spectrometer Telescope on the polar‐orbitingSAMPEXsatellite. The deduced charge state values are in good agreement with the mean values measured directly in previous solar energetic particle events at much lower energies of ∼1 MeV nucleon−1, with inferred equilibrium source temperatures of typically 2×106K. This result provides additional evidence that solar energetic particles in gradual‐type events consist of accelerated coronal material. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50991

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have analyzed the geomagnetic transmission of solar energetic Fe ions at ∼200–600 MeV/nuc during the great solar energetic particle (SEP) events of 1989 September–October. By comparing fluences from the Chicago charged‐particle telescope onIMP‐8 in interplanetary space and from NRL’s Heavy Ions in Space (HIIS) experiment aboardLDEFin low‐Earth orbit, we obtain a mean ionic charge ⟨Q⟩=14.2±1.4. This result is significantly lower than ⟨Q⟩ observed at ∼1 MeV/nuc in impulsive events, and suggests that neither acceleration at the flare site nor flare‐heated plasma significantly contributes to the high‐energy Fe ions we observe. But it agrees well with the ⟨Q⟩ observed in gradual SEP events at lower energies, demonstrating that acceleration by CME‐driven shocks is the primary SEP production mechanism in gradual events even at these very high energies. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50992

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The solar cosmic ray Ground‐Level Enhancement (GLE) observed on 11 June 1991 was mildly anisotropic with a velocity dispersive onset. The anisotropy determined by comparing the flux observed by ‘‘forward viewing’’ high latitude neutron monitors with the flux observed by ‘‘reverse viewing’’ high latitude neutron monitors had an approximate 2‐to‐1 ratio at the GLE maximum. The relativistic proton flux anisotropy persisted through most of the GLE suggesting an extended high energy injection of particles. Using improved modeling techniques we have fitted a shock acceleration spectrum to both the neutron monitor observations and high energy (350 to 550 MeV) spacecraft data. The shock acceleration spectrum used to fit the observations has a differential rigidity slope of −4.62 at 1 GV at the GLE maximum implying a shock compression ratio of 2.237. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50946

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have found evidence for fluxes of energetic electrons in interplanetary space on board the ISEE‐3/ICE spacecraft which we interpret as the decay products of neutrons generated in a solar flare on 1980 June 21. The decay electrons arrived at the spacecraft shortly before the electrons from the flare and can be distinguished from the latter by their distinctive energy spectrum. The time profile of the decay electrons is in good agreement with the results from a simulation based on a scattering mean free path derived from a fit to the flare electron data. The comparison with simultaneously observed decay protons and a published direct measurement of high‐energy neutrons places important constraints on the parent neutron spectrum. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50947

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Whereas the majority of researchers accept the important role of shocks in accelerating particles at the Sun and in the heliosphere, there remain many details to be determined. In this paper the sizes of coronal shocks required by prompt solar particle events are compared with sizes of interplanetary shocks determined frominsitumeasurements. Energetic particle observations imply the existence of shocks extending at least 300° whereas interplanetary shocks at 1 AU extend at most about 180°. The observations can be understood if the longitudinal extents of shocks evolve as they propagate outwards from the Sun. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50948

出版商:AIP    

年代:1996

数据来源: AIP