Dissertation
A HaloSat X-ray analysis of the North Polar Spur
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2020
DOI: 10.17077/etd.005553
Abstract
\textit{HaloSat} is the first mission funded by NASA’s Astrophysics Division to use the CubeSat platform. Using three co-aligned silicon drift detectors, the \textit{HaloSat} observatory measures 0.4 - 7 keV X-ray emission from astrophysical sources. We describe the design and construction of the \textit{HaloSat} science payload, which continues to perform well after almost two years in orbit.
We chose 333 pointings to maximize sky coverage and minimize sources of bright X-ray contamination in the halo fields. We detail the software developed for scheduling science operations in order to maximize the scientific output from the \textit{HaloSat} mission. Our science operations have yielded {\it HaloSat} measurements that are reliable, consistent, and repeatable.
We present spectral analysis of fourteen {\it HaloSat} fields spanning the entirety of an X-ray emitting feature known as the North Polar Spur (NPS). NPS emission is well-described by two thermal components with temperatures $\rm kT_{cool}\approx0.087\,keV$ and $\rm kT_{hot}\approx\,0.28\,keV$. We note the first evidence of a temperature gradient in the NPS hot component. We evaluate distance estimates of 0.4 kpc and 8.0 kpc for the NPS.
The energy $\approx\,6\,\times\,10^{54}$ erg and age $\approx\,10^{8}$ years are reasonable for an NPS 8.0 kpc away associated with the Fermi bubbles, a pair of enormous gamma-ray features believed to arise from energetic outflows from the Galactic center. The pressures we find are consistent with a 10 $\mu$G magnetic field and the density $\approx\,2\,\times\,10^{-3}\rm\,cm^{-3}$ are consistent with an association with the Fermi bubbles. The NPS serves as a tracer of the energetic past of the Galactic center and is a visible relic of the types of feedback that influence the evolution of galaxies in our universe.
Details
- Title: Subtitle
- A HaloSat X-ray analysis of the North Polar Spur
- Creators
- Daniel M LaRocca
- Contributors
- Philip Kaaret (Advisor)Steven Spangler (Committee Member)Cornelia Lang (Committee Member)Casey DeRoo (Committee Member)Keith Jahoda (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Summer 2020
- DOI
- 10.17077/etd.005553
- Publisher
- University of Iowa
- Number of pages
- x, 127 pages
- Copyright
- Copyright 2020 Daniel M LaRocca
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 120-127).
- Public Abstract (ETD)
HaloSat is a type of small satellite known as a CubeSat that is roughly the size a large shoe box and is currently in orbit around the Earth. Here, I detail information about building the HaloSat science instrument, which contains three detectors that allow us to measure the energy of astrophysical X-rays. Extremely hot plasma and other astrophysical objects emit X-rays with energies that can be used to determine various physical properties.
I have been in charge of scheduling the science operations for HaloSat. To maximize sky coverage and avoid objects that would contaminate our observations, I chose the specific locations of our HaloSat halo viewing fields. Also, I developed software to plan and schedule the HaloSat observations.
Using HaloSat, I have taken the first observations of the North Polar Spur in its entirety with moderate spectral resolution. The North Polar Spur is an enormous cloud of several million-degree plasma that spans the sky. With our observations, I measured the physical properties of the North Polar Spur. These properties suggest that it is an enormous object of Galactic scale, and hints at a huge outflow of energy from the center of our Milky Way galaxy. The North Polar Spur is an ancient astrophysical relic, which unveils the energetic past at the center of our galaxy and reveals the mechanisms involved in creating these enormous structures.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9983987997702771
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