Unveiling the Transient Radio and Millimeter Sky

Abstract

The study of astrophysical transients has grown to encompass some of the most violent and extreme physical processes in the cosmos. From the explosive deaths of stars in supernovae to their destruction in tidal disruption events and the as of yet mysterious origin of fast radio bursts (FRBs), the radio sky provides an unparalleled opportunity to study these events in great detail and to gain insight into the unique physics that drive them. In this thesis, we explore these cosmic death throes and the insight afforded by radio and millimeter observations.

First, we present detailed radio and X-ray observations of the first relativistic tidal disruption event, uniquely tracking the evolution toward Newtonian expansion at late times. We then turn our attention to FRBs, focusing initially on the question of host galaxy localizations which have largely hindered progress towards understanding FRB progenitors. Building on the discovery of the first localized FRB coincident with a persistent radio source in a dwarf galaxy, we then present a novel study examining the properties of 20 similar radio sources discovered in nearby dwarf galaxies, and suggest that such sources may serve as signposts for at least some FRBs.

Next, we focus on the rare class of superluminous supernovae (SLSNe), using radio and millimeter observations as unique probes of their underlying central engines. We present the first discovery of radio emission coincident with a SLSN, and demonstrate that the data are fully consistent with central engine powered emission, providing direct evidence for a central engine in one of these sources for the first time. We expand our study of SLSNe by presenting the largest survey of radio and millimeter observations of SLSNe in addition to a subset of long-duration gamma-ray bursts (LGRBs). We present a series of models that self-consistently describe the optical and radio/millimeter properties of these events. Using high time-resolution radio observations, we also present a novel search for FRBs directly from the source positions. We additionally use these observations to place constraints on the level of obscured star formation in the host galaxies of SLSNe and LGRBs, with direct implications for their progenitors.

Finally, we turn to the impending era of wide-field cosmic microwave background (CMB) surveys and explore the utility of these experiments for transient discovery. Indeed while time-domain studies at long wavelengths have focused primarily on the centimeter band, as we show, the next generation of CMB surveys will open a new window for transient science at millimeter wavelengths.

The transient radio and millimeter sky represents a largely unexplored frontier, with observations poised to shed light on transient progenitor models, the formation and evolution of jets and outflows, and the explosion environments for a wide range of sources. This thesis demonstrates the unique capabilities of radio and millimeter observations for studies of astrophysical transients, including how next generation facilities will revolutionize our view of the dynamic and violent universe.