Shocks, Jets, and Emerging Nebulae: Direct Detection and Characterization of Extragalactic Radio Transients in the VLA Sky Survey

Citation

Dong, Dillon Zhejun (2023) Shocks, Jets, and Emerging Nebulae: Direct Detection and Characterization of Extragalactic Radio Transients in the VLA Sky Survey. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/xwy9-tc17. https://resolver.caltech.edu/CaltechTHESIS:04042023-210926442

Abstract

For most of their lives, massive stars and supermassive black holes evolve steadily, changing only gradually on human timescales. But on occasion, these cosmic engines erupt, lighting up their surroundings like flashes in the dark. Under the right conditions, the eruptions can manifest as slow radio transients, rising and fading on timescales of weeks to decades. By finding these transients and observing their evolution, we can study otherwise inaccessible aspects of the engines' lives, and piece together their influence on their surroundings.

Until recently, most of our knowledge of slow radio transients came from follow-up observations of explosions first discovered as optical and high-energy transients. This avenue of discovery, while illuminating, provides an indelibly incomplete picture of the radio transient landscape. Moreover, each successful follow-up detection typically comes at the cost of many unsuccessful attempts (measured in both telescope and human time).

My thesis helps address these issues by finding and characterizing transients directly in radio surveys. By applying novel transient detection techniques to data from the Very Large Array Sky Survey (VLASS), I produced the first uniformly selected sample of radio transients associated with local universe galaxies. The 64 transients in my sample have roughly doubled the total number of directly detected slow radio transients in the literature. This sample has enabled the first volume-limited characterization of the demographics of extragalactic slow radio transients. It has also facilitated the discovery of two previously unseen transient types: the merger of a compact object with a massive star and a decades-old emerging pulsar wind nebula.

These early results used only ~15% of the currently available data from VLASS and focused only on extragalactic transients at low redshift. By applying the same techniques to the full survey, I have found ~2000 new transients, increasing the number of known slow radio transients (detected by any means) by a further order of magnitude. With this new sample, my collaborators and I are beginning to shift the study of slow radio transients from the domain of single-object deep-dives to the domain of statistical samples.

Thesis Files