Publication Date

2025

Advisor(s) - Committee Chair

Gordon Emslie, Michael Carini, Ivan Novikov

Degree Program

Department of Physics and Astronomy

Degree Type

Master of Science

Abstract

Solar flares are powerful explosions that take place on the Sun, equivalent to a billion atomic bombs, and eject billions of tons of material into space. Flares that reach Earth can disrupt power grids and damage satellite communication systems, presenting challenges for our national security. Studying solar flares is crucial to better understand and prepare for these events.

During a solar flare, electrons are accelerated into the surrounding plasma. The interaction between electrons and heavier particles within the plasma causes the emission of powerful X-rays. Studying X-rays from solar flares can, therefore, provide insight into the accelerated electrons that produce them, allowing for a deeper understanding of solar flare processes.

The Spectrometer Telescope for Imaging X-rays (STIX) instrument onboard the Solar Orbiter mission observes the X-ray emission from solar flares. Using an indirect imaging technique, where we invert the spatial Fourier transform of the source, the X-ray data recorded by STIX can be used to reconstruct an X-ray image of the solar flare. Alternatively, we can get the Fourier transform of the electron flux by performing a spectral inversion on the Fourier transform in count space, and then the inverse Fourier transform provides images of the electron flux.

Electron flux images show the location and energy of electrons within a solar flare. Each image is proportional to the product of the density of accelerated electrons at a specified energy and the density of the plasma into which they are injected. Evaluating these densities separately could provide insight into the processes of a solar flare, but the electron maps contain information only on their product. To overcome this problem, a centroid analysis on the electron maps was performed to evaluate the target density separately.

Specifically, a centroid analysis method performed on the electron maps for the May 8th, 2021 solar flare produced an average target density of 5.8 × 1011 cm−3. Using this, together with the observed electron spectrum, the average density of accelerated electrons was shown to be 1.2 × 105 cm−3. Then, using a simple 1-D acceleration model, the ratio between the accelerated electron density and the target density was used to find an electric field of 7 × 10−5 V cm−1 and an average accelerated electron energy of 42 keV.

The energy output of the May 8th, 2021 solar flare was approximately 1030 erg. This energy value was then used to derive a magnetic field of B = 120 G. The electric and magnetic fields are then used to find the average thickness of a current sheet d = 3600 cm. From this length value and the dissipation timescale (τ = 60 s), the conductivity of the plasma was found to be σ = 4 × 1014 s−1, with a magnetic diffusivity of η = 2 × 105 cm2 s−1. Thus, the solar flare had an increased diffusivity and decreased conductivity compared to coronal plasma (η = 300 cm2 s−1 and σ = 2×1017 s−1). The energy stored between the approaching fields is on the order of 1024 erg. It follows that the observed energy of the flare requires approximately 300,000 current sheets.

Disciplines

Physical Sciences and Mathematics | Physics

Download

Included in

Physics Commons

Share

COinS