The Landscape of Relativistic Stellar Explosions

Citation

Ho, Anna Yen Qin (2021) The Landscape of Relativistic Stellar Explosions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/99s8-vj17. https://resolver.caltech.edu/CaltechTHESIS:07132020-190219502

Abstract

For the last half-century, relativistic outflows accompanying the final collapse of massive stars have predominantly been detected via high-energy emission (i.e., gamma-ray bursts, or GRBs). From wide-field optical and radio time-domain surveys, there have been hints of related phenomena at lower energies (e.g., X-ray flashes). For my thesis, I used the Zwicky Transient Facility to conduct the first large-scale optical survey dedicated to finding relativistic stellar explosions. I successfully detected a suite of GRB-related phenomena without relying on a GRB trigger, and followed them up with facilities across the electromagnetic spectrum including ALMA: relativistic afterglows at cosmological distances, broad-lined Ic (Ic-BL) supernovae with X-ray and radio emission, and fast-luminous transients powered by circumstellar interaction. Based on the rate of fast (intra-night) optical transients, I showed that a "clean" jet seems central to the phenomenon of collimated energetic outflows, i.e., there is no evidence for afterglow-like optical transients whose area (sky) rate greatly exceed the classical GRB rate. With a radio and millimeter-wave investigation of AT2018cow, and the discovery of a similar event in ZTF, I established a new class of engine-driven stellar explosions that arise from different progenitors to GRBs and explode embedded in dense circumstellar material. I showed that fast-luminous thermal emission can arise from late-stage eruptive mass-loss and is not necessarily linked to the presence of relativistic ejecta, complicating searches for choked jets in Ic-BL SNe. My work sets the stage for discovering and characterizing relativistic stellar explosions in large numbers during the era of ZTF Phase II, the Large Synoptic Survey Telescope (LSST), and millimeter-band facilities like ALMA and NOEMA.

Thesis Files