摘要:

Relativistic solar proton events have been prolific during the 22nd solar cycle. With improved measurement techniques and time resolutions several unusual characteristics have been observed in the intensity‐time profiles of these events as recorded by ground‐based neutron monitors. In particular several events exhibit an unusual initial anisotropic spike recorded by stations viewing into or through a narrow cone of asymptotic directions. A similar structure was observed during the 19th solar cycle associated with solar activity from the same heliolongitude range on the solar disk. Any solar particle acceleration and/or interplanetary propagation models must be able to explain these type of intensity‐time profiles. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50949

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We analyze neutron monitor data of solar cosmic rays in order to obtain information about their sources. We use three methods for these data analysis. As result, we obtain a set of evidences for two separate solar cosmic rays sources that we call as prompt and delayed components. We attempt here to substantiate a two sources scenario for the generation of both components. For the prompt component source, we suggest regular acceleration in a neutral current sheet. For the delayed one, we propose acceleration by magnetosonic wave turbulence. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50950

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a time dependent analysis of the &ggr;‐ray line spectra recorded by the PHEBUS instrument on board GRANAT during the 1991 June 1 flare. For each studied spectrum we determine the electron bremsstrahlung continuum and the &ggr;‐ray line fluences &Fgr;1.1–1.8and &Fgr;4.1–7.6, in the 1.1–1.8 MeV and 4.1–7.6 MeV bands respectively, as well as their ratioR=&Fgr;1.1–1.8/&Fgr;4.1–7.6. We find that the power law index of the bremsstrahlung continuum in the 0.6–10 MeV band is 2.6±0.1 and that it remains constant with time. The characteristic value ofR, estimated for the spectrum accumulated over the whole event duration is about 4 but, surprisingly,Rincreases from a value of ∼3 to a value of ∼7 during the decay phase of the event. In order to interpret these findings we have compared the measured values ofRwith those obtained by using calculations of deexcitation &ggr;‐ray line spectra performed for different interacting particle spectra and compositions. We show that the high value ofRand its large variation with time are inconsistent with a thick target &ggr;‐ray line source and that a thin target model is the appropriate one. This is consistent with an earlier study of the 1991 June 1 event which indicates that the observed nuclear line emission is produced in a coronal source. We finally argue that the increase ofRwith time strongly suggests an impulsive flare composition for the accelerated particles and the further enrichment of the heavy nuclei abundances as the flare progresses. For thin target interactions such an enrichment is most probably due to the acceleration process itself. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50951

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We review measurements of ten narrow &ggr;‐ray lines in 19 X‐class solar flares observed by the Solar Maximum Mission spectrometer from 1980 to 1989 (1) which showed that abundances of elements in the flare plasma are grouped with respect to their first ionization potentials (FIP), indicated that both the Ne/O and C/O line ratios are dependent on the spectral index of accelerated particles, and suggested that the range in low‐FIP/high‐FIP line ratios is similar to that in comparing coronal and photospheric compositions. We confirm this range in variability using the (Mg+Si+Fe)/Ne line ratio, which is not strongly dependent on the spectrum of accelerated ions. We also use measurements of the positronium continuum and annihilation line to show that &ggr;‐rays from flares with the lowest low‐FIP to high‐FIP ratios were produced deep in the chromosphere where the abundances should be close to photospheric. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50952

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We used SMM gamma ray data from 19 solar flares to study ambient elemental abundances in the solar atmosphere. We found that the abundance ratios of low FIP (first ionization potential) to high FIP elements (Mg/O, Si/O, Fe/O) are enhanced relative to photospheric abundances and may vary around their respective coronal values. For the high FIP elements (C, O, Ne) we showed that: (i) The gamma ray data allows a good determination of the C to O abundance ratio; the data are consistent with a C/O which does not vary from flare to flare; and the best fit value is C/O=0.4. (ii) The derived value of Ne/O (∼0.25) is higher than the coronal value of 0.15 obtained from solar energetic particle data and some EUV and X‐ray observations of photospheric material. To avoid Ne/O higher than 0.3 a steep accelerated particle energy spectrum extending down to about 1 MeV/nucl is needed. This implies that a large fraction of the available flare energy is contained in accelerated ions. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50953

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Spectral observations of the 4 June 1991 solar flare obtained with the Oriented Scintillation Spectrometer Experiment (OSSE) on board theComptonGammaRayObservatory(CGRO) are used to determine the interaction rate of the accelerated protons by fitting two‐minute spectra with a narrow nuclear‐deexcitation line template. The lines are produced primarily when accelerated protons interact with ambient solar material and thus reveal the proton interaction rate. The OSSE observations provide the only direct measurements of this emission during the intense portion of the 4 June flare. A subset of the data is then used to determine individual fluxes of 8 narrow &ggr;‐ray lines. These preliminary fluxes are compared to line fluxes determined for 19 flares obtained with theSolarMaximumMissionGamma Ray Spectrometer (SMM/GRS). Ambient elements with low first‐ionization potentials (FIP) appear to be enhanced relative to those with higher FIP (as compared to the photosphere) similar to the enhancement found previously for the 27 April 1981SMMflare. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50954

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The flare of 16 December 1988 is one of the most intense gamma‐ray line events that the Gamma‐Ray Spectrometer (GRS) on SMM has recorded. It proceeded in several well separated bursts. By taking the fluences of selected energy bands, the spectrum of the primary particles can be determined. We find that it changes from burst to burst, suggesting even different acceleration mechanisms. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50955

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We review some of the highlights of the COMPTEL measurements of solar flares. These include images of the Sun in &ggr; rays and neutrons. One of the important features of the COMPTEL instrument is its capability to measure weak fluxes of &ggr; rays and neutrons in the extended phase of flares. These data complement the spectra taken with the COMPTEL burst spectrometer and the telescope during the impulsive phase of flares. We focus our attention on some of these general capabilities of the instrument and the latest results of two long‐duration &ggr;‐ray flares, i.e., 11 and 15 June 1991. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50956

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Two gamma‐ray flares were observed with a gamma‐ray spectrometer and two X‐ray imagers aboardYOHKOH. The gamma‐ray flare on 27 October 1991 showed strong narrow deexcitation lines and two bright hard X‐ray sources. We discuss a gamma‐ray production site from comparison the gamma‐ray (4.5–6.8 MeV) time profile with the hard X‐ray (53–93 keV) time profile of each hard X‐ray bright source. The gamma‐ray lines are thought to be produced at one of the two hard X‐ray sources. The gamma‐ray flare on 3 December 1991 showed strong continuum extending about 8 MeV without detectable gamma‐ray line. It implies that electrons were preferentially accelerated to relativistic energies. The rapid enhancement in hard X‐ray (53–93 keV) emission was observed nearly simultaneously with the large change in flaring loop structures. It suggests that the electrons were efficiently accelerated by strong electric field induced by the rapid variation in the magnetic field. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50957

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

During the solar flare events on 11 and 15 June 1991, COMPTEL measured extended emission in the neutron capture line for about 5 hours after the impulsive phase. The time profiles can be described by a double exponential decay with decay constants on the order of 10 min for the fast and 200 min for the slow component. Within the statistical uncertainty both flares show the same long‐term behaviour. The spectrum during the extended phase is significantly harder than during the impulsive phase and pions are not produced in significant numbers before the beginning of the extended emission. Our results with the measurements of others allow us to rule out long‐term trapping of particles in non‐turbulent loops to explain the extended emission of these two flares and our data favour models based on continued acceleration. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.50958

出版商:AIP    

年代:1996

数据来源: AIP