Measurements of X-Ray Selected AGN and Novel Superconducting X-Ray Detectors

Citation

Eckart, Megan Elizabeth (2007) Measurements of X-Ray Selected AGN and Novel Superconducting X-Ray Detectors. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SZAB-0Y07. https://resolver.caltech.edu/CaltechETD:etd-06072007-130804

Abstract

Major astrophysical advances typically come through combining new observational approaches with new technologies. This thesis involves work on both fronts, combining observational work using data from the Chandra X-ray Observatory and Keck Observatory with novel superconducting detector development to further technology for future observatories.

The subject of the first part of this thesis is the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program, a survey using Chandra data selected to probe the dominant contributors to the 2-10 keV cosmic X-ray background. SEXSI covers more than 2 square degrees of sky and employs optical photometric and spectroscopic followup of sources discovered in archival Chandra fields. The resulting sample consists of 1034 hard X-ray-selected sources with R-band optical-followup imaging, and optical spectroscopy for 477 of the sources, filling the gap between wide-area, shallow surveys and the deep, pencil-beam surveys. The vast majority of the 2-10 keV-selected sample are AGN with redshifts between 0.1 and 3. We discuss results from our survey, including the spectroscopic properties of hard X-ray sources and the relationship between X-ray and optical properties of our sources. In addition, we present infrared data from the Spitzer Space Telescope that cover a subset of the Chandra fields, which allows us to explore the relative strengths of Chandra and Spitzer as black-hole finders.

The second part of this thesis focuses on microwave kinetic inductance detectors (MKIDs), a superconducting detector technology that has breakthrough potential for providing megapixel imagers with several eV energy resolution for use in future X-ray missions. These detectors utilize simple, thin-film lithographed microwave resonators as photon detectors in a multiplexed readout approach. X-ray absorption in a superconductor creates quasiparticle excitations, with number proportional to the X-ray energy. The surface impedance of a superconductor changes with the quasiparticle density, and if operated at T << T_c, extremely small changes in the surface impedance can be measured using the thin-film resonant circuit and microwave readout techniques. This provides a sensitive detector with excellent energy resolution.

MKIDs offer the advantage over many other cryogenic detector technologies that they can be easily multiplexed by coupling many resonators to a single microwave transmission line. In addition, the readout electronics can be operated at room temperature, a significant advantage for space applications. The practical application of MKIDs for photon detection requires a method of efficiently coupling the photon energy to the MKID. To this end we have been studying MKIDs in a strip detector architecture. The second part of this thesis presents our results using strip detectors with tantalum absorbers coupled to aluminum MKIDs.

Thesis Files