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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The remarkable outflows from the galactic microquasar SS433

Jeffrey, Robert January 2016 (has links)
In this thesis, I present 4 new, high-resolution observations of the Galactic microquasar SS 433, obtained from the Very Long Baseline Array (VLBA). I show that we can resolve the same ejecta in successive observations separated by ~ 35 d. I will demonstrate a method to uniquely determine launch vectors of the jet bolides, and I use this unprecedented baseline in time to show that the expansion rate of these bolides may reach 0.03c. I also present the first scientific results from the study of the radio jets in a unique set of historic observations of SS 433: the 39 images that comprise the 2003 VLBA movie of Mioduszewski et al. (2004). This unmatched time sampling allows us to see daily changes in the dynamics of SS 433's jets. I present evidence that these observations caught SS 433 as it transitioned from quiescence into a flare, and I show that this manifests itself as an increase in both the jet launch speed and the brightness of the jet bolides. Using these data, I examine the evolution of the particle energies, densities and magnetic fields within the bolides. We see that the estimates of the mass-loss rates via the jets cannot be reconciled with the those inferred from X-ray or optical data, if we posit equipartition of energy in synchrotron emitting plasma. The time resolution of the 2003 data allows us to observe the flux evolution of the jet bolides, and I show that the bolides undergo a power law decay as t<sup>−2.8</sup>. Lastly, I examine X-ray monitoring data from the Swift/BAT satellite and the MAXI All-Sky- Monitor. From these lightcurves, I examine the geometry of the X-ray emission from close to the compact object itself, and I discuss SS 433's place within the current paradigm of accretion in microquasars. Throughout, we will see that it is the accessible time scales of the SS 433 phenomenon that allow us to learn about its exciting, complex physics.
2

Investigating the Microquasar SS 433 and the PeVatron Candidate MGRO J1908+06 with a Novel Extended Source Analysis Method

Kleiner, Tobias Kai 10 June 2024 (has links)
Die Herkunft galaktischer sehr hochenergetischer und ultrahochenergetischer kosmischer Strahlung bleibt rätselhaft, aber Studien weisen auf zahlreiche galaktische Quellen namens PeVatrons hin, die Teilchen auf Petaelektronenvolt-Energien beschleunigen können, darunter Pulsarwindnebel, Supernovareste und Mikroquasare. Die Untersuchung der Gammastrahlung bei Giga- und Teraelektronenvolt-Energien bietet entscheidende Einblicke in ihre Eigenschaften und erweitert unser Verständnis hochenergetischer astrophysikalischer Phänomene. Diese Arbeit analysiert Daten des VERITAS-Gammastrahlenobservatoriums, bestehend aus vier 12-Meter-Tscherenkow-Teleskopen in Arizona, um ein umfassendes Verständnis von zwei galaktischen Quellen zu liefern: MGRO J1908+06, ein potenzieller PeVatron-Kandidat, und SS 433, ein Mikroquasar. MGRO J1908+06 wurde bereits in verschiedenen Wellenlängen untersucht, wobei mehrere potenzielle Ursprünge der Strahlung identifiziert wurden. Diese Arbeit führt eine umfassende Neuuntersuchung seiner ausgedehnten Gammastrahlenemissionen durch, um präzisere Abschätzungen des Gammastrahlenflusses zu liefern und frühere Ergebnisse zu aktualisieren. Die Untersuchung deutet auf einen möglichen Ursprung der Gammastrahlung sowohl aus einem Relikt eines Pulsar-Windnebels als auch aus einem neuen Pulsar-Windnebel im Feld von MGRO J1908+06 hin. Erstmals wird in den VERITAS-Daten eine signifikante Gammastrahlenemission von SS 433 festgestellt. Es werden die Gammastrahlen der Jets bei größeren Abständen und ihre Morphologie untersucht, und TeV-Spektren werden generiert. Modelle zeigen einen leptonischen Ursprung dieser Emissionen, ohne dass eine signifikante Gammastrahlenemission in der Nähe des Schwarzen Lochs oder Anzeichen für Variabilität beobachtet werden. Ausblickend präsentiert die Arbeit Untersuchungen zur Optimierung der Eigenschaften des Cherenkov-Teleskop-Array Observatoriums, mit Fokus auf die Platzierung von Illuminatoren und Abschattungseffekte zwischen Teleskopen. / The origins of galactic very-high energy and ultra-high energy cosmic rays remain elusive. Recent studies propose the existence of PeVatrons, galactic sources capable of accelerating particles to Petaelectronvolt energies, such as pulsar wind nebulae, supernova remnants, and micro-quasars. Exploring gamma-ray emission at Giga- and Teraelectronvolt energies offers crucial insights into their properties, enriching our understanding of high-energy astrophysical phenomena. This thesis focuses on analysing data from the VERITAS gamma-ray observatory, comprising four 12-meter imaging atmospheric Cherenkov telescopes in Arizona. Employing 3D maximum-likelihood analysis methods, the study aims to provide a comprehensive understanding of two extended galactic sources: MGRO J1908+06, a potential PeVatron candidate, and SS 433, a microquasar. MGRO J1908+06, though unidentified, has been scrutinized across various wavelengths, with several potential counterparts identified previously. This thesis undertakes a re-analysis of its extended gamma-ray emission, leveraging updated analysis methods and recent VERITAS observations. The improved analysis method provides a more accurate estimate of the gamma-ray flux, revising prior VERITAS flux estimates and suggesting a scenario involving both relic and new pulsar wind nebulae. Regarding SS 433, significant gamma-ray emission is detected in VERITAS data for the first time. The morphological properties of the gamma-ray emission regions seen at larger distances along the jets are examined, and their TeV spectra are constructed. Modelling supports a leptonic origin of these emissions, with no significant gamma-ray emission observed near the black hole or any indication of variability. Looking ahead, the thesis presents investigations aimed at optimizing the characteristics of the Cherenkov Telescope Array Observatory, focusing on illuminator placement and mutual shadowing effects to enhance telescope positioning within the array.

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