ALBERT

Notes: Abstract We have derived the energy spectrum of accelerated protons and nuclei at the site of the June 21, 1980 limb flare by a new technique, using observations of the time-dependent flux of high-energy neutrons at the Earth. We find that this energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra have been previously derived using observations of 4–7MeV-to-2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep (αT ∼- 0.02) to produce any significant amount of radiation from π meson decay. We suggest that the observed 〉10 MeV gamma rays from the June 21, 1980 flare are bremsstrahlung of relativistic electrons.

Notes: Abstract Positron-electron pair radiation is examined as a mechanism that could be responsible for the impulsive phase emission of the 5 March, 1979 transient. Synchrotron cooling and subsequent annihilation of the pairs can account for the energy spectrum, the very high brightness, and the ∼0.4 MeV feature observed from this transient, whose source is likely to be a neutron star in the supernova remnant N49 in the Large Magellanic Cloud. In this model, the observed radiation is produced in the skin layer of a hot, radiation-dominated pair atmosphere, probably confined to the vicinity of the neutron star by a strong magnetic field. The width of this layer is only about 0.1 mm. In this layer, ∼1012 generations of pairs are formed (by photon-photon collisions), cooled and annihilated during the ∼0.15 s duration of the impulsive phase. The very large burst energy implied by the distance of the LMC, and its very rapid release, are unsolved problems. We mention, nonetheless, the possibility of neutron star vibrations, which could transport the energy coherently to the surface, heat the atmosphere mechanically to a hot, pair-producing temperature, and have a characteristic damping time roughly equal to the duration of the impulsive phase.

Notes: Abstract The depth dependence of the production of neutrons and capture gamma-ray line emission are calculated by Monte Carlo simulation of the nuclear processes taking place when flare-accelerated ions interact with the solar atmosphere. The calculations also give the heliocentric-angular dependence of the 2.223 MeV neutron capture line emission as a function of accelerated-ion energy spectrum and angular distribution. These results are compared with observations to determine the energy spectrum shape and total ion number for various flares.

Notes: Abstract We briefly describe our recent Monte Carlo calculations of the energy and angular distributions of neutrons escaping from the solar atmosphere. Comparing the calculation results with measurements of the neutron flux from the flares, we determined the angular distribution and energy spectrum of the accelerated ions. We also describe our calculations of the time dependence of the 2.223 MeV line emission, which provide a sensitive measure of the photospheric 3He abundance. We find that the SMM measurements of the time dependence of the 2.2 MeV line emission from the flare of 1982 June 3 imply a 3He/H ratio of (2.3±1.2)×10−5 at the 90% confidence level.

Notes: Abstract It has previously been suggested that the energy for the optical emission of solar flares was provided by ionization losses of accelerated particles in the flares. We show that nuclear interaction of these particles would also produce fluxes of secondary neutrons and gamma rays detectable at the earth. A comparison of the expected intensities of these secondaries with the present upper limit intensities during solar flares shows that such an origin from the optical emission energy is consistent with the measured limits.

Notes: Abstract Center of mass-center of figure offsets are known for the Earth, Moon, Mars and Venus. Such an offset requires a density distribution asymmetric about the center of mass. Observational evidence indicates that the terrestrial, lunar and Martian offsets result from crusts of variable thickness rather than lateral density inhomogeneities and that the thickness variations are more likely caused by internal convection than impact.

Notes: Abstract The theory of gamma-ray production in solar flares is treated in detail. Both lines and continuum are produced. The strongest line predicted at 2.225 MeV with a width of less than 100 eV and detected at 2.24±0.02 MeV, is due to neutron capture by protons in the photosphere. Its intensity is dependent on the photospheric 3He abundance. The neutrons are produced in nuclear reactions of flare accelerated particles which also produce positrons and prompt nuclear deexcitation lines. The strongest prompt lines are at 4.43 MeV from 12C and at ∼6.2 from 16O and 15N. These lines result from both direct excitation and spallation. The widths of individual prompt lines are determined by nuclear kinematics. The width of the 4.43 MeV line is ∼100 keV and that of the 6.2 MeV feature is ∼300 keV. Both these lines have been observed from a solar flare. Other potentially observable lines are predicted at 0.845 and 1.24 MeV from 56Fe, at 1.63 MeV principally from 14N and 20Ne, at 1.78 MeV from 28Si, at ∼5.3 MeV from 15O and 15N, and at 7.12 MeV from 16O. The widths of the iron lines are only a few keV, while those of the other lines are about 100 keV. The only other observed line is at 0.511 MeV from positron annihilation. The width of this line is determined by the temperature, and its temporal variation depends on the density of the ambient medium in the annihilation region. Positrons can also annihilate from the 3 S state of positronium to produce a 3-photon continuum below 0.511 MeV. In addition, the lines of 7Li and 7Be at 0.478 keV and 0.431 keV, which have kinematical widths of ∼30 keV, blend into a strong feature just below the 0.511 MeV line. From the comparison of the observed and calculated intensities of the line at 4.4 MeV to that of the 2.2 MeV line it is possible to obtain information on the spectrum of accelerated nuclei in flares. Moreover, from the absolute intensities of these lines the total number of accelerated nuclei at the Sun and their heating of the flare region can be estimated. We find that about 1033 protons of energies greater than 30 MeV were produced in the 1972, August 4 flare. The gamma-ray continuum, produced by electron bremsstrahlung, allows the determination of the spectrum and number of accelerated electrons in the MeV region. From the comparison of the line and continuum intensities we find a proton-to-electron ratio of about 10 to 102 at the same energy for the 1972, August 4 flare. For the same flare the protons above 2.5 MeV which are responsible for the gamma-ray emission produce a few percent of the heat generated by the electrons which make the hard X-rays above 20 keV.

Notes: Abstract Recent gamma-ray line observations and their interpretations are reviewed and prospects for future line detections are discussed.