Interferometric Millimeter Observations of the High Energy Universe

Citation

Yadlapalli, Nitika (2024) Interferometric Millimeter Observations of the High Energy Universe. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/g8fs-5q44. https://resolver.caltech.edu/CaltechTHESIS:08172023-032920075

Abstract

This thesis explores what can be accomplished in the ways of time-domain astrophysics with a variety of scales of millimeter interferometry. I touch upon techniques in instrumentation, theory, observation, and computation, showcasing the breadth and richness of the field.

The transient millimeter sky is largely comprised of synchrotron sources whose physical properties are just beginning to be revealed. We are entering an age where new wide-field surveys will exponentially increase the number of known transients, including the first wide-field millimeter survey capable of significant transient detections. As we approach this era, resources dedicated to monitoring and follow-up become increasingly more important.

A significant part of my work involves design and commissioning for a new single baseline millimeter interferometer at the Owens Valley Radio Observatory called SPRITE. Uniquely positioned as a dedicated transient follow-up telescope, SPRITE has the ability to observe nearby transients with a relatively high cadence. In this thesis, I also highlight two specific classes of sources for which millimeter observations may be particularly interesting. I present predictions for millimeter emission from supernovae interacting with dense circumstellar media and discuss their rates of detection in upcoming surveys. I additionally present lower frequency spatially-resolved radio observations of an X-ray binary in an active state.

On the other extreme, this thesis also explores the use of very long baseline interferometry to investigate how high resolution images of supermassive black holes vary over the timescale of a year. In 2017, the Event Horizon Telescope Collaboration (EHTC) observed the supermassive black hole in nearby galaxy M87, producing the first resolved image of the shadow of a black hole and potentially revealing intra-day variability of the observed synchrotron emission around the shadow. I present work on the imaging and preliminary analysis of the 2018 epoch of EHT observations of the black hole in M87, and discuss the EHTC’s conclusions of intra-day and year-long variations in the images.