Physics
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aipc..410...17s&link_type=abstract
The fourth compton symposium. AIP Conference Proceedings, Volume 410, pp. 17-36 (1997).
Physics
5
Stellar Activity, Gamma-Ray
Scientific paper
Observations by the Compton GRO are providing fundamental insights into the high-energy physics of solar flares. Most of the analyses have been made of the flares emitted by active region number 6659 in 1991 June. Hard X-ray pulses in flares show energy dependent delays of up to ~200 ms due to time of flight, consistent with the location of an acceleration region above the soft X-ray loop and an impact some in the footpoints. Comparison of electron bremsstrahlung and 80 GHz synchrotron emissions provides information on magnetic field strengths in the corona. Temporal variations as short as 0.1 s are observed at energies above 10 MeV constraining acceleration models. Protons are observed to be accelerated up to energies in excess of a few GeV and relativistic ions are still present in sufficient intensities up to eight hours after the impulsive phase of the 11 June flare to be detected in the γ rays they produce at energies above 50 MeV. Comparison of the energy dependence of time profiles suggests that particle acceleration is continuing hours after the impulsive phase and that trapped particles do not provide the dominant emission. Individual γ-ray lines are resolved and provide information on the accelerated ion spectra and the ambient elemental composition. The 1991 June 4 flare produced the highest line fluence observed to date and had an ambient abundance close to that observed in the corona. A rather high accelerated α/p ratio, ~0.5, is inferred from the line measurements. The energy deposited in ions >1 MeV/AMU is at least an order of magnitude larger than that of electrons in this event. Temporal variation is observed in the accelerated electron/ion ratio over a broad energy range, in the ambient abundances, and in the spectral hardness in the June flares. Comparisons of the neutron capture and de-excitation lines provide measurements of the 3He/H ratio, and information on the 4He/H ratio in the photosphere. We also report on a search for hard X-rays from selected stars.
Murphy Ronald J.
Ryan J. J.
Share Gerald H.
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