An X-Ray Study of Gravitational Lenses

Open Access
Dai, Xinyu
Graduate Program:
Astronomy and Astrophysics
Doctor of Philosophy
Document Type:
Date of Defense:
August 11, 2004
Committee Members:
  • Gordon Paul Garmire, Committee Chair
  • George Chartas, Committee Chair
  • Michael Eracleous, Committee Member
  • Robin Bruce Ciardullo, Committee Member
  • Lee S Finn, Committee Member
  • gravitational lenses
  • active galactic nuclei
  • cosmology
  • dark matter
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.