Library

Notes: Abstract Response of Alma-Ata neutron monitor for solar neutrons from the 15 June 1991 was studied. We considered this response as a test for various scenarios of proton acceleration during the flare. The analysis of neutron monitor is an evidence in favour of the assumption of two acts of proton acceleration at impulsive and post-impulsive phases of the flare.

Notes: Abstract A joint analysis of neutron monitor and GOES data is performed to study the production of high-energy neutrons at the Sun. The main objects of the research are the spectrum of 〉50 MeV neutrons and a possible spectrum of primary (interacting) protons which produced those neutrons during the major 1990 May 24 solar flare. Different possible scenarios of the neutron production are presented. The high magnitude of the 1990 May 24 neutron event provided an opportunity to detect neutron decay protons of higher energies than ever before. We compare predictions of the proposed models of neutron production with the observations of protons on board GOES 6 and 7. It is shown that the ‘precursor’ in high-energy GOES channels observed during 20:55–21:09 UT can be naturally explained as originating from decay of neutrons in the interplanetary medium. The ratio of counting rates observed in different GOES channels can ensure the selection of the model parameters. The set of experimental data can be explained in the framework of a scenario which assumes the existence of two components of interacting protons in the flare. A hard spectrum component (the first component) generates neutrons during a short time while the interaction of the second (soft spectrum) component lasts longer. Alternative scenarios are found to be of lesser likelihood. The intensity-time profile of neutron - decay protons as predicted in the framework of the two-component exponential model of neutron production (Kocharov et al., 1994a) is in an agreement with the proton profiles observed on board GOES. We compare the deduced characteristics of interacting high-energy protons with the characteristics of protons escaping into the interplanetary medium. It is shown that, in the 100–1000 MeV range, the spectrum of the second component of interacting protons was close to the spectrum of the prompt component of interplanetary protons. However, it is most likely that, at ∼300 MeV, the interacting proton spectrum was slightly softer than the spectrum of interplanetary protons. An analysis of gamma-ray emission is required to deduce the spectrum of interacting protons below 100 MeV and above 1 GeV.

Notes: Abstract The energetic particle instrument ERNE on-board SOHO started its observations on December 15, 1995. The low-energy sensor of ERNE, LED, is capable of measuring particles in the energy range from 1 to 10 MeV nucl-1. From the beginning of the year 1996 until May 22, 1996, LED-observations included four energetic particle events above threshold intensities. An energetic particle event caused by a corotating interaction region that accelerated protons upto ∽ 10 MeV, was observed during January 20–25. Another similar particle event occured on May 6–12. The events were separated by four solar rotation periods. They had similar time profiles, but the one in May had a harder spectrum and a lower intensity level. The 4He-to-proton ratios were in accordance with the solar wind value. Energetic particles observed during April 22–23 and May 14–17 were accelerated at the Sun. The first one was apparently an outcome from an active region observed on the west limb by telescopes on-board SOHO. Protons were detected at energies from 1 to ∽10 MeV. For this event, the4He-to-proton ratio in the range 1.5–5 MeV nucl-1 was ∽ 3%. No 3He ions were detected. The period of May 14–15 was, in contrast, extremely 3He-rich: it had a3He-to-proton ratio of 1.5 ± 0.6 and a 3He-to- 4He ratio as high as ∽ 8. The period of May 14–17 comprised at least three individual, one-day-long events. The first two events were 3He-rich, while the last one seemed to have a normal composition.

Notes: Abstract In this paper, we are primarily concerned with the solar neutron emission during the 1990 May 24 flare, utilizing the counting rate of the Climax neutron monitor and the time profiles of hard X-rays and γ-rays obtained with the GRANAT satellite (Pelaezet al., 1992; Talonet al., 1993; Terekhovet al., 1993). We compare the derived neutron injection function with macroscopic parameters of the flare region as obtained from theHα and microwave observations made at the Big Bear Solar Observatory and the Owens Valley Radio Observatory, respectively. Our results are summarized as follows: (1) to explain the neutron monitor counting rate and 57.5–110 MeV and 2.2 MeV γ-ray time profiles, we consider a two-component neutron injection function,Q(E, t), with the form $$Q(E,t) = N_f {\text{ exp[}} - E/E_f - t/T_f ] + N_s {\text{ exp[}} - E/E_s - t/T_s ],$$ whereN f(s),E f(s), andT f(s) denote number, energy, and decay time of the fast (slow) injection component, respectively. By comparing the calculated neutron counting rate with the observations from the Climax neutron monitor we derive the best-fit parameters asT f ≈ 20 s,E f ≈ 310 MeV,T s ≈ 260 s,E s ≈ 80 MeV, andN f (E 〉 100 MeV)/N s (E 〉 100 MeV) ≈ 0.2. (2) From the Hα observations, we find a relatively small loop of length ≈ 2 × 104 km, which may be regarded as the source for the fast-decaying component of γ-rays (57.5–110 MeV) and for the fast component of neutron emission. From microwave visibility and the microwave total power spectrum we postulate the presence of a rather big loop (≈ 2 × 105 km), which we regard as being responsible for the slow-decaying component of the high-energy emission. We show how the neutron and γ-ray emission data can be explained in terms of the macroscopic parameters derived from the Hα and microwave observations. (3) The Hα observations also reveal the presence of a fast mode MHD shock (the Moreton wave) which precedes the microwave peak by 20–30 s and the peak of γ-ray intensity by 40–50 s. From this relative timing and the single-pulsed time profiles of both radiations, we can attribute the whole event as due to a prompt acceleration of both electrons and protons by the shock and subsequent deceleration of the trapped particles while they propagate inside the magnetic loops.

Notes: Abstract This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (‘focusing-free’) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is ‘renormalized’ by the focusing.

Notes: Abstract We analysed the solar particle event following the 9 July 1996 solar flare. High-energy protons were detected by the ERNE instrument on board SOHO. Anisotropy of arriving protons revealed very peculiar non-monotonic development. A short period of almost isotropic distribution was imbedded into the prolonged period of beam-like distribution of 14–17 MeV protons. This implies the existence of a narrow magnetic channel with a much smaller mean free path than in the surrounding quiet solar wind plasma. We used Monte Carlo simulations of interplanetary transport to fit the observed anisotropies and intensity–time profiles. Proton injection and transport parameters are estimated. The injection scenario is found to be very close to the scenario of the 24 May 1990 event, but the intensity and the interplanetary transport parameters are different. The extreme anisotropy observed implies prolonged injection of high-energy protons at the Sun and at the interplanetary shock front, and either a very large mean free path (≥ 5 AU) outside the slow transport channel, or alternatively, a somewhat smaller mean free path (≈2 AU) and enhanced focusing between the Sun and the Earth.

Notes: Abstract The first increase in neutron monitor count rate during the ground-level event on 24 May 1990 was interpreted by Shea et al. (1991) as a consequence of an arrival of flare neutrons. Debrunner et al. (1991) rejected the neutron hypothesis and proposed that the first neutron monitor increase was due to the arrival of primary protons. We have show that neutron monitor data do not contradict the hypothesis of a neutron origin of the first increase of ground-level event on 24 May 1990.

Notes: Abstract Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to 0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data.

Notes: Abstract We have considered secondaries produced by accelerated particles trapped in a coronal magnetic structure as well as by those precipitating down into dense regions of the solar atmosphere. We have calculated time profiles and generation anisotropy for π 0-decay γ-radiation, nuclear γ-ray lines and 〉10 MeV electron bremsstrahlung in a flare magnetic arch. We have shown that as primary particles move inside a magnetic arch in an inhomogeneous atmosphere the secondary emission turns out to be anisotropical, even if the acceleration process is an isotropical one. On the other hand, the anisotropy of the acceleration process not only influences the directivity of secondary emission but also its intensity decay rate. The exact as well as simple approximate calculation techniques for the angular and temporal characteristics of γ-ray emission are discussed. These techniques may be applied to considering the generation process of another kind of secondary product in flare loops.

Notes: Abstract We consider the generation of high-energy neutron and π 0-decay γ-quanta inside magnetic loops on the Sun. Using Monte Carlo simulations we investigate the influence of pitch-angle diffusion upon the characteristics of secondary emission. We consider various cases of diffusion on exterior MHD-turbulence as well as on Alfvén waves generated by accelerated particles through the cyclotron instability. We compare the calculated results to SMM flare observations and show that the observational data on the 3 June, 1982 flare do not contradict the assumption of the impulsive phase acceleration of all the protons, given that the energy spectrum of the accelerated particles is an energy power law.