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Published November 1994 | Published
Journal Article Open

Neutron and electromagnetic emissions during the 1990 May 24 solar flare


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; Talon et al., 1993; Terekhovet al., 1993). We compare the derived neutron injection function with macroscopic parameters of the flare region as obtained from the Hα 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 exp[−E/E_f−t/T_f]+N_s exp[−E/E_s−t/T_s], Where N_(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 as T_f ≈ 20 s, E_f ≈ 310 MeV, T_s ≈ 260 s,E_s ≈ 80 MeV, and N_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.

Additional Information

© 1994 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 22 April, 1994; in revised form 15 July, 1994. We thank the referee, Dr H. Debrunner, for helpful comments. We are grateful to Prof. Grant E. Kocharov who urged us to study the neutron emission from this flare. We thank Prof. John A. Simpson for providing the Climax neutron monitor data, Dr Dale E. Gary for helpful comments on the interpretation of microwave data obtained at the Owens Valley Radio Observatory, and Drs Andrei M. Bykov and Valery M. Ostryakov for discussion of particle acceleration and propagation problems. We also wish to thank Dr Alan P. Patterson for the observation of the white-light flare at Big Bear Solar Observatory. Observations at Big Bear Solar Observatory have been funded by NASA grant NAGW- 1972 and observations at Owens Valley Radio Observatory by NSF grants ATM-9311416 and AST- 9314929 to the California Institute of Technology. One of us (LGK) was supported by NSF grant ATM-9122023 during his visit to the Big Bear Solar Observatory. Work at the University of Chicago has been supported by NSF grant ATM-9215122. One of us (IGU) is grateful to the American Astronomical Society for financial support of his work.

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September 15, 2023
September 15, 2023