Blazars are a subclass of active galactic nuclei whose observable characteristics are generated by relativistic jets of high-energy plasma with trajectories closely aligned to the line of sight. This orientation results in extreme observed phenomena, such as ultraluminous emission, high amplitudes of variability, and high degrees of optical linear polarization. Furthermore, blazars are the most common extragalactic sources of γ-ray photons and have been proposed as sources of high-energy neutrinos.
Long-timescale monitoring of blazars has revealed relatively quiescent states interspersed with active states featuring dramatic brightening events, with timescales ranging from months to years. New, high-time-resolution observations of blazars are revealing dramatic variability on timescales as short as several minutes, the physical drivers of which are not well understood. In this dissertation, I focus on observational signatures that can potentially identify these mechanisms. To characterize this variability, I combine observations of blazars from many telescopes, obtaining a comprehensive view of events occurring in the jets.
Using the Very Long Baseline Array, I investigate moving and quasi-stationary features in the parsec-scale jets of 38 blazars. I find that the flow speeds, orientation, brightness temperatures, and opening angles of the jets in flat-spectrum radio quasars (FSRQs), BL Lacertae type objects (BL Lac objects), and radio galaxies (RGs) are statistically different, with FSRQs having the highest speeds and smallest viewing angles. Focusing on a typical source of each subclass, I characterize the optical variability observed at 2-min cadence (with the Transiting Exoplanet Survey Satellite), at gamma-ray energies (Fermi Large Area Telescope), X-ray energies (NICER, NuSTAR, and Swift satellites), and optical (ground-based instruments, especially, the Perkins telescope), including linear polarization measurements.
I find that the minimum timescale of RG variability is longer than those of the FSRQ and BL Lac object, and is likely caused by changes in the accretion disk. In contrast, the variability in the FSRQ and BL Lac object can be associated with shocks, magnetic reconnections, and turbulence in the jet. The unprecedented availability of data, which promises to expand in the future, represents a new phase of observational astronomy that provides valuable information on changes in the jets of blazars.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/48018 |
| Date | 06 February 2024 |
| Creators | Weaver, Zachary Roger |
| Contributors | Marscher, Alan P. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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