Hard x-ray observations of the extragalactic sky: the High Energy Focusing Telescope and the Serendipitous Extragalactic X-ray Source Identification survey

Abstract

Extending the energy range of high sensitivity astronomical x-ray observations to the hard x-ray band (10--100 keV) is important for the study of nonthermal emission mechanisms and heavily obscured sources. This thesis, in two parts, describes the development of the High Energy Focusing Telescope (HEFT), a focusing telescope for the hard x-ray band, and the Serendipitous Extragalactic X-ray Source Identification (SEXSI) survey, a degree-scale x-ray/optical survey of sources detected in the Chandra hard band (2--7 keV). HEFT is a balloon-borne x-ray telescope that is expected to have its first flight in the fall of 2003. The telescope will be among the first to focus x-rays at energies greater than 20 keV. HEFT's mirrors use graded multilayers -- thin film coatings ($sim 1 mu$m) that enhance high energy reflectance via constructive interference. In the first half of the thesis, I describe the optimization algorithm that I developed for x-ray optics and how I applied this algorithm to the design of the HEFT optics. In addition, I present x-ray measurements that verify the HEFT multilayer coating designs at energies where the telescope will operate. The SEXSI survey complements Chandra deep-field surveys by covering a much larger area of the sky, but to a shallower x-ray flux limit. For the SEXSI survey, we use public data from the Chandra archive to compile a catalog of extragalactic sources detected in the 2--7 keV band. We identify the optical counterparts to the x-ray sources and obtain their optical spectra (400--1000 nm). Presently SEXSI includes 30 Chandra fields, covering roughly 2 square degrees and yielding over 1200 x-ray sources to a flux limit of $10^{-15}$--$10^{-13}$ ergflux. In the second part of the thesis, I present results from 10 fields for which we have substantial spectroscopic coverage.