Date of Award
12-2019
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Physics and Astronomy
Committee Member
Stefano Marchesi
Committee Member
Dieter Hartmann
Committee Member
Mark Leising
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 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 chapter 1, the objective of this thesis is introduced. In chapter 2, SNRs and PWNe are explained in detail with a focus on the Vela SNR - the closest composite SNR to Earth. In chapter 3, we discuss the main instruments used to obtain the γ-ray and X-ray data, namely XMM-Newton and the Fermi-LAT. Chapter 4 describes the data reduction process and spectral analysis and a multi- wavelength description of 2FHL J0826.1−4500 is presented in chapter 5. Chapter 6 tests the spectral energy distribution (SED) of the source, attempting to determine the dominant parent particle population to better understand its emission mechanisms. In chapter 7 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?
Recommended Citation
Eagle, Jordan Lynn, "Investigation of a Candidate for Cosmic Ray Acceleration" (2019). All Theses. 3195.
https://tigerprints.clemson.edu/all_theses/3195