An X-Ray Study of Gravitational Lenses
Open Access
- Author:
- Dai, Xinyu
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 11, 2004
- Committee Members:
- Gordon Paul Garmire, Committee Chair/Co-Chair
George Chartas, Committee Chair/Co-Chair
Michael Eracleous, Committee Member
Robin Bruce Ciardullo, Committee Member
Lee S Finn, Committee Member - Keywords:
- gravitational lenses
active galactic nuclei
cosmology
dark matter - Abstract:
- Gravitational lensing of distant quasars by intervening galaxies, where multiple images are formed, is a spectacular phenomenon in the universe. With the advent of Chandra, it is possible to resolve for the first time in the X-ray band lensed quasar images with separations greater than about 0.3 arcsec. We use lensing as a tool to study AGN and Cosmology. The X-ray band probes the inner most regions of the central engines of AGN. The lensing flux magnification, ranging from a few to ~100, enables us to obtain high signal-to-noise spectra and light-curves of high redshift quasars with less observing time and allows us to search for changes in quasar spectroscopic properties and X-ray flux variability over three orders of magnitude in intrinsic X-ray luminosity. One surprising result that we found in the sample of radio-quiet, high-redshift lensed quasars is a possible Gamma-L_x relation, which may indicate that high redshift quasars are accreting close to their Eddington limits. We also use the microlensing effects induced by stars in the lensing galaxies to study the structure of the accretion discs of AGN, which cannot be resolved by current instruments. In the case of Q2237+0305, where an X-ray microlensing event was detected, we concluded that the broad Iron line region which is affected by the GR and SR effects is smaller than the X-ray continuum region. Finally we use gravitational lensing as a tool to study Cosmology. By measuring the time-delays between different lensed images it is possible to constrain the Hubble constant independently from other techniques. We have successfully measured time-delays in two lensed systems and have placed a lower limit in a third one.