arXiv subjects
Publications and source records attributed to Olaf Wucknitz.
We discuss a simple parameter degeneracy in lens models which follows directly from the well known mass sheet degeneracy and prevents determining the radial mass distribution from lensing alone for many systems. For cosmological important systems like 1115+080 it is shown that no exact value of H0 can be determined without assuming a mass index beta.
We present first results from five years of spectrophotometric monitoring of the bright double QSO and gravitational lens HE 1104-1805. The quasar has varied considerably over this time, while the emission line fluxes appear to have remained constant. We have constructed monochromatic continuum light curves for components A and B, finding that B leads the variability. A quantitative analysis with the Pelt method gives a best estimate for the light travel time delay of about 0.73 years, although a value as low as 0.3 cannot yet be excluded. We discuss possible models for the QSO-lens configuration and use our measured time delay to predict the redshift of the lens, z_d. Finding that most likely z_d < 1, we can rule out the hitherto favoured values of z_d = 1.32 or 1.66. A new candidate is an absorption system at z=0.73, but the lens could also be an elliptical not detected in absorption.
We have obtained new BVR-band images of the gravitationally lensed QSO pair HE 2149-2745 A,B (QSO redshift z=2.033; angular separation theta_AB=1.71 arcsec), under 1 arcsec seeing conditions. Subtraction of a scaled point-spread-function reveals an extended object of angular size comparable to theta_AB, and R magnitude of 20.4 lying between and equidistant to the QSOs. The geometry of the system leads us to interpret this object as the lensing agent responsible for the double QSO images. A fit to the galaxy surface brightness profile indicates an elliptical galaxy, which is further supported by the absence of Mg II in absorption. The lensing galaxy is not detected in B and V. We discuss possible lens models for this geometry constrained by our observations and consequences for the mass and redshift of the lens.