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Thesis

ABSTRACT

COMPTEL MEASUREMENTS OF NUCLEAR GAMMA-RAY LINES IN SOLAR FLARES

By Raid M. Suleiman
University of New Hampshire, September 1995

This thesis presents the results of a study of nuclear deexcitation gamma-ray lines and the neutron capture line in solar flares as measured by the burst detectors of COMPTEL. As a result of this search, the COMPTEL solar flare catalog was constructed and about thirty solar flares were confirmed. A detailed analysis of the gamma-ray spectra for six of these flares (i.e., June 9, 11, October 24, 27I, 27II, and December 20 of 1991) is presented. They were measured with the high range burst detector of COMPTEL, on board Compton Gamma-Ray Observatory (CGRO). An overview of the gamma-ray lines is given. Photon spectra for the above six flares are given. A modeling for the bremsstrahlung and the nuclear continuum is estimated. Estimates of the accelerated proton spectrum and the spectral indices are given based on the fluence of the 2.223 MeV neutron capture line relative to the integrated fluence in the 4-7 MeV band.

A comparison of the calculated photon spectra and the proton spectra with the theoretical picture of the flare phenomena is presented.

We find that observed flux of the above six flares can be explained by accelerated particles having Bessel function spectra with wide range of indices (alpha T is greater than 0.008 and less or equal to 0.168). We find that for the flare of June 11 1991 that the spectrum hardens in time as seen in the fluence ratio after the impulsive phase. The spectral indices of June 9 and 11 time averaged are with agreement with those calculated by Ramaty et al. (1993).

We find in two of the six flares namely October 24 and 27 1991 that the Ne line at 1.634 MeV is more intense than the neutron capture line or any other nuclear deexcitation line. An enhancement of the Ne is found in the tail phase of June 9 1991 flare relative to that of the impulsive phase. The anomalous intensity of the ambient 1.634 MeV line can be explained by either a soft spectrum or a local abundance enhancement.

 

 

 

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