Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..855l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 2, p. 855-862
Astronomy and Astrophysics
Astronomy
12
Directivity, Fluence, Gamma Ray Astronomy, Particle Acceleration, Size Distribution, Solar Flares, Spectrum Analysis, Variations, X Ray Astronomy, Bremsstrahlung, Coulomb Collisions, Electron Beams, H Alpha Line, Solar Maximum Mission, Spectral Energy Distribution, Spectrometers, Venera Satellites
Scientific paper
We have studied 72 solar flares simultaneously observed by the Gamma-Ray Spectrometer (GRS, 0.3-1 MeV) and the Hard X-Ray Burst Spectrometer (HXRBS, 30-500 keV) on the Solar Maximum Mission (SMM). Using the spectral analysis results, we studied spectal and size distribution center-to-limb variations for both instruments. The GRS observations show significant center-to-limb variations in both spectral and size distributions, while HXRBS observations show insignificant variations. In general, the GRS spectra are harder than the HXRBS spectra, and their difference increases from center to limb, suggesting that a flattening of the spectrum above 300 keV is inevitable for the gamma-ray emissions. We corrected for the effect of spacecraft pointing and combined HXRBS and GRS data to obtain spectra over the energy range of 0.03-1 MeV. The fluences at various energies were calculated and normalized to the total fluence of the burst to measure the directivity. It is found that the directivity increases with increasing energy, from 1.1 at 50 keV to 6.5 at 1 MeV. These results are consistent with anisotropic electron beams and the physics of Coulomb collision and bremsstrahlung.
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