The starting conditions for an optically small solar gamma ray flare

It is suggested that optically small gamma-ray flares result from gradual pre-flare acceleration of protons over approximately 1,000 s by a series of magnetohydrodynamic shocks in the low corona. A fraction of the accelerated protons are trapped in the corona where they form a seed population for future acceleration. If the shock acceleration is sufficiently rapid proton energies may exceed the gamma-ray production threshold and trigger gamma-ray emission. This occurs without the total flare energy being necessarily large. Magnetic field geometry is an important parameter

Spectral and spatial properties of solar microflares

Solar microflares are studied using both hard ( 28 keV) and soft (3.5 to 8.0 keV) X-ray observations. The soft X-ray events have durations 3 m at 0.1x maximum intensity, and typically have similar rise and decay times. The fastest decay observed was 15 s (1/e). Soft and hard X-ray intensities are uncorrelated. The events are very compact, consistent with a projected area approximately 8 x 8 inches. They are normally not associated with H alpha or type 3 emissions and their time profiles suggest a thermal origin at the top of the chromosphere. If the primary energy release site is in the corona, an energy transfer agent consistent with the observations is a non-thermal proton beam

Observations of cosmic ray electrons between 2.7 and 21.5 MeV

Intensity of 2.7 to 21.5 MeV electrons in interplanetary space from Explorer 34 measurement

Electronics implementation of the solar neutron experiment

The electronic equipment design and function are discussed for the solar neutron counter experiment. Circuit diagrams are included

Electron versus Proton Timing Delays in Solar Flares

Both electrons and ions are accelerated in solar flares and carry nonthermal energy from the acceleration site to the chromospheric energy loss site, but the relative amount of energy carried by electrons versus ions is subject of debate. In this {\sl Letter} we test whether the observed energy-dependent timing delays of 20-200 keV HXR emission can be explained in terms of propagating electrons versus protons. For a typical flare, we show that the timing delays of fast (\lapprox 1 s) {\sl HXR pulses} is consistent with time-of-flight differences of directly precipitating electrons, while the timing delays of the {\sl smooth HXR} flux is consistent with collisional deflection times of trapped electrons. We show that these HXR timing delays cannot be explained either by $\le 1$ MeV protons (as proposed in a model by Simnett \& Haines 1990), because of their longer propagation and trapping times, or by $\approx 40$ MeV protons (which have the same velocity as $\approx 20$ keV electrons), because of their longer trapping times and the excessive fluxes required to generate the HXRs. Thus, the HXR timing results clearly rule out protons as the primary generators of $\ge 20$ keV HXR emission.Comment: 7 pages, TEX type, AASTeX macros, 1 Figure, to appear in Astrophysical Journal Letters, accepted 1996 July 2

A large area detector for neutrons between 2 and 100 MeV

A neutron detector sensitive from 2 to 100 MeV is described. The detector is designed for high altitude balloon flight to measure the flux, energy and direction of albedo neutrons from the earth and to search for solar neutrons. A neutron scatter from a proton is required in each of two liquid scintillator tanks spaced 1 meter apart. The energy of the recoil proton in the first tank is obtained from pulse height analysis of the scintillator output. The energy of the recoil neutron is obtained from its time of flight between the tanks. The detector has been calibrated with 15.3 MeV neutrons and mu mesons. The minimum detectable flux is 10(-4) neutron/sq cm/sec at a counting rate of one per minute; the energy resolution is 12% at 15 MeV and 30% at 100 MeV. The angle between the incoming neutron and the recoil neutron is measured to + or - 10 deg

Bright Points and Subflares in UV Lines and in X-Rays

We have analysed an active region which was observed in Halpha (MSDP), UV lines (SMM/UVSP), and in X rays (SMM/HXIS). In this active region there were only a few subflares and many small bright points visible in UV and in X rays. Using an extrapolation based on the Fourier transform we have computed magnetic field lines connecting different photospheric magnetic polarities from ground-based magnetograms. Along the magnetic inversion lines we find 2 different zones: 1. a high shear region (less than 70 degrees) where subflares occur 2. a low shear region along the magnetic inversion line where UV bright points are observed