Date of Award

Spring 2001

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

James Ryan


Measurements of high energy emission from solar events can lead to an understanding of the solar energetic particle acceleration mechanism(s). Although the energy source of these mechanisms is known to reside in the solar magnetic field, the details of the acceleration process(es) have continued to elude researchers. By observing the particle emission at the upper limits of the spectrum, essential information about the location and the nature of the acceleration mechanism(s) can be obtained.

Milagrito was an extensive air shower observatory which operated as a prototype for the larger Milagro instrument. It operated from February 1997 to May 1998. Although Milagrito was originally designed as a high energy (>100 GeV) water-Cherenkov gamma ray observatory, it could also be used to study solar energetic particles (SEPs). In a scaler mode, it was sensitive to muons and small showers from hadronic primary particles above ∼3 GeV. Simultaneously, Milagrito also operated in a shower mode which had increased sensitivity due to its ability to reconstruct event directions, but this mode required primary particles of higher energy. In its scaler mode, Milagrito registered a ground level enhancement associated with the 6 November 1997 SEP event and X9 solar flare. At its peak, the enhancement was 22x background RMS fluctuations. Based on comparisons to neutron monitor and satellite data, we conclude that the differential flux of energetic protons from this event followed a rigidity-power-law spectrum which became steeper above a few GeV, and that the acceleration site was at ∼2 solar radii. This altitude is relatively low in the corona, but it is well above the flare site.