From Tantrums to Transformations: AGN Transients Discovered with the Zwicky Transient Facility
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This dissertation work has consisted of searches for extreme AGN-related outbursts during Phase I of the Zwicky Transient Facility (ZTF) survey, which has been a ground-breaking wide-field instrument for the real-time detection and regular cadence monitoring of transients in the Northern Sky. Transients found to be nuclear through photometric filtering were vetted by humans and coordinated for prompt follow-up with various rapid robotic, spectroscopic, and high energy resources, to understand the nature of the galaxy centers undergoing flares and the appearance of spectral features. Findings from this unprecedentedly high-volume data stream were often serendipitous, and led to surprising new avenues for study, including 1) the establishment of a new observational class of quiescent galaxies caught turning into quasars, 2) the discovery of a preponderance of smooth and high-amplitude optical transients hosted in NLSy1s, and 3) a framework for distinguishing extreme AGN variability from other transients in AGN. We present the results of these observations, including candidates for TDEs in AGN, changing-look AGN caught "turning-on", as well as members of the new emerging observational class of flares in Narrow-Line Seyfert 1 (NLSy1) galaxies associated with enhanced accretion (Trakhtenbrot et al. 2019). We compared the properties of these samples of flares to previously reported changing-look quasars and Seyfert galaxies, confirmed that they are a unique observational class of transients related to physical processes associated with the central supermassive black hole's accretion state, and considered the observations in the context of the physical interpretations for a range of related transients from the literature. With these unique sample sets, we also aim to understand why we have found certain galaxy types to preferentially host the sites of such rapid enhanced flaring activity, and attempt to map out the innermost environment of the accretion events. These pathfinding studies enabled with ZTF have the potential to guide how these exceptional moments of AGN evolution will be systematically discovered in future large area surveys such as the Vera C. Rubin Observatory.