Radio Burst and Circular Polarization Studies of the Solar Corona at Low Frequencies A thesis submitted to fulfill requirements for the degree of Doctor of Philosophy by Patrick I. McCauley School of Physics Faculty of Science arXiv:1912.01747v1 [astro-ph.SR] 4 Dec 2019 University of Sydney Australia October, 2019 Dedicated to Julie. Thanks for everything. i Declaration of originality To the best of my knowledge, this thesis contains no copy or paraphrase of work published by another person, except where duly acknowledged in the text. This thesis contains no material which has previously been presented for a degree at the University of Sydney or any other university. I certify that the authorship attribution statements on the next page are correct. Patrick I. McCauley As supervisor for the candidature upon which this thesis is based, I confirm that the originality and authorship attribution statements above and on the next page are correct. Iver H. Cairns iii Included Papers and Attribution Chapters2{4 are peer-reviewed journal articles for which I was primarily re- sponsible. They are reproduced as published aside from minor typographical changes for consistency. In addition to general manuscript comments, the main contributions of my coauthors were as follows. Cairns: general supervision and guidance, advice on experimental design and interpretation. Morgan: assis- tance with data reduction and advice on instrumental effects. Gibson: as- sistance with observation { model comparisons. Harding: assistance with flux calibration. Lonsdale & Oberoi: facilitation of data collection and advice on data reduction. White: advice on results interpretation. Mondal: independent data validation. Lenc: advice on polarimetry and instrumental effects. Chapter2 Type III Solar Radio Burst Source Region Splitting due to a Quasi-separatrix Layer Patrick I. McCauley, Iver H. Cairns, John Morgan, Sarah E. Gibson, James C. Harding, Colin Lonsdale, and Divya Oberoi Published in The Astrophysical Journal, 851:151 (2017) Chapter3 Densities Probed by Coronal Type III Radio Burst Imaging Patrick I. McCauley, Iver H. Cairns, and John Morgan Published in Solar Physics, 293:132 (2018) Chapter4 The Low-Frequency Solar Corona in Circular Polariza- tion Patrick I. McCauley, Iver H. Cairns, Stephen M. White, Surajit Mondal, Emil Lenc, John Morgan, and Divya Oberoi Published in Solar Physics, 294:106 (2019) (Blue and red text denote internal and external hyperlinks, respectively.) v Other Works The following is a reverse-chronological list of other peer-reviewed articles, ex- cluding conference proceedings, that I have authored or coauthored. Items 1 { 8 were published or submitted during my PhD candidature. 1. Beardsley, A. P., et al. (57 coauthors, including McCauley, P. I.), Science with the Murchison Widefield Array: Phase I Results and Phase II Opportunities. Publica- tions of the Astronomical Society of Australia, in press, 2019 2. Cairns, I. H., et al. (15 coauthors, including McCauley, P.), Comprehensive Char- acterization of Solar Eruptions with Remote and In Situ Observations, and Modeling: The Major Solar Events on 4 November 2015. Solar Physics, in press, 2019 3. Mohan, A., McCauley, P. I., Oberoi, D., & Mastrano, A., A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes. The Astrophysical Journal, 883:45, 2019 4. Rahman, M., McCauley, P. I., & Cairns, I. H., On the Relative Brightness of Coronal Holes at Low Frequencies. Solar Physics, 294:7, 2018 5. Kleint, L., Wheatland, M. S., Mastrano, A., & McCauley, P. I., Nonlinear Force- Free Modeling of Magnetic Field Changes at the Photosphere and Chromosphere Due to a Flare. The Astrophysical Journal, 865:146, 2018 6. Jones, G. H., et al. (19 coauthors, including McCauley, P.), The Science of Sun- grazers, Sunskirters, and Other Near-Sun Comets. Space Science Reviews, 214:20, 2018 7. Cairns, I. H., Lobzin, V. V., Donea, A., Tingay, S. J., McCauley, P. I., et al. (46 coauthors), Low Altitude Solar Magnetic Reconnection, Type III Solar Radio Bursts, and X-ray Emissions. Scientific Reports, 8:1676, 2018 8. Lenc, E., et al. (28 coauthors, including McCauley, P. I.), The challenges of low- frequency polarimetry: lessons from the Murchison Widefield Array. Publications of the Astronomical Society of Australia, 34:e040, 2017 9. Janvier, M., Savcheva, A., Pariat, E., Tassev, S., Millholland, S., Bommier, V., Mc- Cauley, P., McKillop, S., & Dougan, F., Evolution of Flare Ribbons, Electric Cur- rents and Quasi-separatrix Layers During an X-class Flare. Astronomy and As- trophysics, 591:A141, 2016 vii 10. Savcheva, A., Pariat, E., McKillop, S., McCauley, P., Hanson, E., Su, Y., & DeLuca, E. E., The Relation between CME Topologies and Observed Flare Features II: Dynam- ical Evolution. The Astrophysical Journal, 817:43, 2016 11. Savcheva, A., Pariat, E., McKillop, S., McCauley, P., Hanson, E., Su, Y., Werner, E., & DeLuca, E. E., The Relation between CME Topologies and Observed Flare Features I: Flare Ribbons. The Astrophysical Journal, 810:96, 2015 12. Su, Y., van Ballegooijen, A. A., McCauley, P. I., Ji, H., Reeves, K. K., & DeLuca, E. E., Magnetic Structure and Dynamics of the Erupting Solar Polar Crown Prominence on 2012 March 12. The Astrophysical Journal, 807:144, 2015 13. Reeves, K. K., McCauley, P. I., & Tian, H., Direct Observations of Magnetic Re- connection Outflow and CME Triggering in a Small Erupting Solar Prominence. The Astrophysical Journal, 807:7, 2015 14. McCauley, P. I., Su, Y., Schanche, N., Evans, K. E., Su, C., McKillop, S., & Reeves, K. K., Prominence and Filament Eruptions Observed by the Solar Dynamics Observatory: Statistical Properties, Kinematics, and Online Catalog. Solar Physics, 290:1703, 2015 15. Tian, H., et al. (27 coauthors, including McCauley, P.), Prevalence of Micro-Jets from the Network Structures of the Solar Transition Region and Chromosphere. Sci- ence, 346:6207, 2014 16. Raymond, J. C., McCauley, P. I., Cranmer, S., & Downs, C., The Solar Corona as Probed by Comet Lovejoy (C/2011 W3). The Astrophysical Journal, 788:152, 2014 17. Masson, S., McCauley, P., Golub, L., Reeves, K. K., & DeLuca, E., Dynamics of the Transition Corona. The Astrophysical Journal, 787:145, 2014 18. Savcheva, A. S., McKillop, S. C., McCauley, P. I., Hanson, E. M., & DeLuca, E. E., New Sigmoid Catalog from Hinode and the Solar Dynamics Observatory: Statistical Properties and Evolutionary Histories. Solar Physics, 289:3297, 2014 19. McCauley, P. I., Saar, S. H., Raymond, J. C., Ko, Y. -K., & Saint-Hilaire, P., Extreme-Ultraviolet and X-Ray Observations of Comet Lovejoy (C/2011) in the Lower Corona. The Astrophysical Journal, 768:161, 2013 20. Cirtain, J. W., et al. (13 coauthors, including McCauley, P.), Energy Release in the Solar Corona from Spatially Resolved Magnetic Braids. Nature, 493:501, 2013 21. McCauley, P., Mangum, J. G., & Wootten, A., Formaldehyde Densitometry Of Galactic Star-Forming Regions Using The H2CO 3(12)-3(13) And 4(13)-4(14) Tran- sitions. The Astrophysical Journal, 742:58, 2011 viii Acknowledgements This thesis contains work done between 2016 and 2019, but I view it as the culmination of my scientific career to date. I have been very fortunate to interact with many wonderful people along the way, all of whom have helped me in large and small ways to achieve this goal. I will take this opportunity to acknowledge all of them, to the best of my memory, back to my earliest research experiences. First, I am most grateful for the consistent support and encouragement from my family and friends. Particularly from my partner, Julie, my parents, Ken and Carolyn, and my brothers, Nick and Petey. I love you all. Next, I am extremely grateful to all of my immediate supervisors. I first thank my thesis advisor at the University of Sydney, Iver Cairns. Iver consis- tently demonstrates great care and respect for all of his students. He was always supportive and kindly afforded me great freedom in my research direction. I next thank Kathy Reeves and the solar group at the Harvard-Smithsonian Center for Astrophysics. Kathy was a wonderful boss, and the whole group could not have been more supportive. They are responsible for my love of solar physics. I am also grateful to Jeff Mangum at the National Radio Astronomy Observatory. Jeff kindly brought me back to NRAO to finish a summer re- search project that I had failed to complete as an undergraduate. I would not have continued in research without that opportunity. Finally, I thank Harold Butner and William Alexander for supporting me through my first research and outreach experiences at James Madison University, which ultimately led to everything else. In addition to my supervisors, I have been fortunate to collaborate with and receive assistance from many excellent scientists over the years. In alphabet- ical order, I am grateful to Alisdair Davey, Ed DeLuca, Kaitlin Evans, Sarah Gibson, Leon Golub, Natasha Hurley-Walker, Kelly Korreck, Kamen Kozarev, Emil Lenc, Colin Lonsdale, Alpha Mastrano, Don Melrose, Atul Mohan, Surajit Mondal, John Morgan, Nick Murphy, Aimee Norton, Divya Oberoi, John Ray- mond, Steve Saar, Pascal Saint-Hilaire, Jon Sattelberger, Antonia Savcheva, Mike Stevens, Yingna Su, Bill Thompson, Hui Tian, Mark Weber, Mike Wheat- land, Stephen White, and Trae Winter. I have also made many great friends in my scientific journey, including sev- eral people from the previous list. My favorite part of the PhD experience was unquestionably getting to know my wonderful officemates in Sydney: Samira Tasnim, James Harding, Ron Maj, Mozibur Rahman, Fiona Schleyer, Tom Hanly, and Will Trevett. I will miss all of you. In Boston, my fellow support scientists Sean McKillop, Nicole Schanche, and Trish Jibben likewise made my time there infinitely more enjoyable. The same goes for my fellow summer students in Charlottesville: Katy Wyman, Missie Louie, Michael Lam, Jen Shitanishi, Francillia Samuel, and Brian Roper. And from the Astro Lab in Harrisonburg: Dan Simonson, Colin Wilson, Chris Wolfe, and Dillon Trewlany. Finally, I am very grateful to the Australian government for supporting this work through an Endeavour Postgraduate Scholarship.