Date of Award
Program or Major
Doctor of Philosophy
James M Ryan
This dissertation expands the current understanding of the 15 November 1991 X1.5 solar flare. This flare was a well observed event in radio to gamma-ray energies and is the first gamma-ray flare to be extensively studied with the benefit of detailed soft and hard X-ray images. In this work, we add data from all four instruments on the Compton Gamma Ray Observatory (CGRO), spanning 20 keV--300 MeV. From these data we determined that the accelerated electron spectrum above 170 keV is best fit with a power law with a spectral index gamma ≈ -4.6. We determined that the accelerated proton spectrum above 0.6 MeV is also fit with a power law, with spectral index s ≈ -4.5. From these distributions, we computed a lower limit for the energy content of these particles: ∼10 23 ergs for the electrons above 170 keV and ∼1027 ergs for the ions above 0.6 MeV. These particles do not have enough energy to produce the white-light emission observed from this event.
We computed a time constant tau of 26+20-15 for the 2.223 MeV neutron capture line. This is consistent at the 2sigma level with the lowest values of ∼70s found for other flares.
We modeled the impulsive X-ray emission from this flare with a 1D spatial diffusion equation (Ryan and Lee 1991). We assumed a constant magnetic field and that turbulence and collisions affects the transport of particles. For relativistic electrons, we found that X-ray observations during the impulsive phase can be explained if turbulence is present such that the mean free path between interactions is 0.1% of the total loop length. Collisions can be included, but are not necessary. We found that the injection source of accelerated particles is most likely located near the apex of the coronal loop. This model can also explain other features of the X-ray observations.
Arndt, Martina Belz, "X- and gamma -ray observations of the 15 November 1991 solar flare" (2000). Doctoral Dissertations. 2137.