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Investigation of a Candidate for Cosmic Ray Acceleration

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Investigation of a Candidate for Cosmic Ray Acceleration Clemson University TigerPrints All Theses Theses 12-2019 Investigation of a Candidate for Cosmic Ray Acceleration Jordan Lynn Eagle Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_theses Recommended Citation Eagle, Jordan Lynn, "Investigation of a Candidate for Cosmic Ray Acceleration" (2019). All Theses. 3195. https://tigerprints.clemson.edu/all_theses/3195 This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. Investigation of a Candidate for Cosmic Ray Acceleration A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Master of Science Physics by Jordan L. Eagle December 2019 Accepted by: Dr. Marco Ajello, Committee Chair Dr. Mark Leising Dr. Dieter Hartmann Abstract Studies of the non-thermal Galactic source population are essential to understand how and where the bulk of cosmic rays are being accelerated and to understand the mechanisms underlying very high energy (VHE, E>50 GeV) emitters [39, 51]. The plane of the Milky Way is rich with supernova remnants (SNRs) and pulsar wind nebulae (PWNe) which are efficient accelerators of cosmic rays (CRs) - whose interaction with the surrounding photon fields produces energetic γ- rays and neutrinos. SNRs and PWNe are some of the most powerful objects in our Galaxy and because they emit at very high energies (VHE, E>50 GeV), γ-rays represent an excellent probe of the non-thermal astrophysical processes in these objects. Relativistic electrons (i.e. leptons) can produce γ-rays by non-thermal bremsstrahlung or by inverse Compton scattering (IC) on ambient photon fields, whereas protons and heavier nuclei (i.e. hadrons) can generate γ-rays by the process of pion decay, produced in collisions between relativistic hadrons and ambient material. Understanding the particle population responsible for the observed γ-ray emission can provide clues to the potential of CR acceleration as most cosmic rays are made of protons or heavier nuclei ( 10% of all cosmic rays are leptons) so, if it can be established that ∼ the γ-ray emission is hadronic in origin, then we can better understand the likelihood for hadron CR acceleration in VHE objects. In this thesis, we report on the investigation of a very high energy (VHE), Galactic γ-ray source recently discovered at >50 GeV using the Large Area Telescope (LAT) on board Fermi. This object, 2FHL J0826.1 4500, displays one of the hardest >50 GeV spectra (Γγ 1:6) in the 2FHL − ∼ sample, and a follow-up observation with XMM-Newton has uncovered diffuse, soft thermal emission at the position of the γ-ray source. A detailed analysis of the available multi-wavelength data shows that this source is located on the Western edge of the Vela supernova remnant: the observations and the spectral energy distribution modeling support a scenario where this γ-ray source is the ii byproduct of the interaction between the SNR shock and a neutral Hydrogen cloud. If confirmed, this shock-cloud interaction would make 2FHL J0826.1 4500 a promising candidate for efficient − particle acceleration. This work has been recently published in the Astrophysical Journal [30]. In chapter1, the objective of this thesis is introduced. In chapter2, SNRs and PWNe are explained in detail with a focus on the Vela SNR - the closest composite SNR to Earth. In chapter3, we discuss the main instruments used to obtain the γ-ray and X-ray data, namely XMM-Newton and the Fermi-LAT. Chapter4 describes the data reduction process and spectral analysis and a multi- wavelength description of 2FHL J0826.1 4500 is presented in chapter5. Chapter6 tests the spectral − energy distribution (SED) of the source, attempting to determine the dominant parent particle population to better understand its emission mechanisms. In chapter7 we report our conclusions on 2FHL J0826.1 4500 and emphasize important properties that still need to be probed in order to − best answer the underlying question: if 2FHL J0826.1 4500 is an efficient particle accelerator, can − we safely establish if this is a site generating fresh CRs or does the energetic environment favor a scenario where pre-existing CRs are being re-accelerated here? iii Dedication Warning: This section of my thesis is going to be very emotional and possibly cheesy. This work is dedicated to my family: my mom (Jeannie Eagle), my father (John Eagle), and my sister (Jamie Elkhill). These people have seen my bests and my worsts since I've been a living, breathing human being. Clearly, they deserve to own a part of this glory with me. Let me also be a little silly and dedicate this to my animals as well: Ruca, my Beagle, and Mars, my tabby cat. They are very special animals that have been cute, adorable, and loving, even in my darkest of hours. In fact, let's dedicate this to all animals everywhere - thanks for dealing with humans. This one's for you. Back to being serious, I need to emphasize two very special people who 100% are responsible for my even being capable of getting to this point: My father and grandfather (Jim Eagle). To my father, for instilling my sense of wonder in the stars from a small age. For exposing me to the movie Contact (and then later, the book). To this day, I will tell anyone that this movie has a significant impact on my initial decision in choosing physics. Seriously though, Dad, you have been a grand influence in my life and I love you so much! To Jim Eagle, my grandfather, who unfortunately passed away just last year on May, 29, 2018. For your intellect, advice, love, support, and also for raising such an amazing son that I get to call Dad. We argued and discussed politics and science often and even though we may have had wildly different views on some topics, your insight was invaluable. You were well-read and patient. You were thoughtful and kind. You always listened and would respond carefully and wisely. You were always learning, always reading, always asking questions, always passionate to discover more. It made you a wonderful writer, poet, and a thorough student. It made you a marvelous husband and father. If I inherited even half of your qualities, I would consider myself a lucky woman. My grandmother, who this thesis is also dedicated to, was lucky to have you by her side for 62 grand iv years. Grandma (Doris Eagle), I love you both so much and I promise to live in the memory of my grandpa. I will never forget to wonder, to dream, to try it anyways, to travel, to learn, and most importantly, to give it all I've got. Lastly, I can't forget to share this part of my journey with my Oma and Opa. You have been pillars in my life. Thank you for always telling it like it is. Here's to all members of my family who have rooted for me along the way and continue to push me when I get distracted or discouraged. I love you all so much! v Acknowledgments Even though this is in the beginning of the thesis, this part was written last because it is undeniably the most challenging part to attempt to begin to acknowledge those who made this milestone in my career possible. First and foremost, I'd like to thank my co-advisor, Dr. Stefano Marchesi. Stefano has dealt with all of my agitating trouble-shooting (some politely have called it "learning"): the incessant inquiries, errors, re-occurring problems with data reduction, spectral analyses, etc. You name a potential problem and Stefano and I can guarantee we had it and Stefano was always able to fix it. Not only has he been hugely helpful in the learning process of the tasks discussed in this thesis, but his patience is astounding. I want to personally recognize Stefano's willingness to work with me day and night and (somehow) remain calm and patient with me. You have done great things before and during your time at Clemson and I know you will continue to be a great scientist and amazing mentor to many people and projects in Bologna, Italy and beyond. Thank you for everything you have taught me! You have enabled my success at Clemson more than you will ever know. Secondly, I need to give a shout out to my supervisor, Dr. Marco Ajello, who invited me to start on this research project in the first place. I was open-minded to research projects within the astronomy field upon coming to Clemson but, when I learned of Marco's research focus and spoke with him many times regarding his work, I got tunnel vision for this particular topic. I am absolutely in love with the violent nature of these objects; Everyday my work amazes me. The universe is far more unforgiving, tumultuous, and chaotic than we could ever have dreamed and I am lucky enough to be able to characterize these phenomena. It almost makes me feel sorry for those who didn't chose this career path because they are missing out on all of the fun and especially, the wonder. Marco has been supportive, kind, and patient as well. He is active in his role as supervisor, mentor, organizer, researcher { not just with me and my research project but with all of his graduate vi students and within the scientific community. You are an inspiration, Marco! You juggle so much and are still dazzlingly successful.
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