This note addresses possible applications of the Tikhonov regularization to image reconstruction of gravitational lens systems. Several modifications of the regularization algorithm are discussed. Our illustrative example is the close quadruple gravitational lens QSO 2237+0305 (Einstein Cross). The restored image of the lens is decomposed into two parts - the quasar components and the background galaxy.
Extremely light bosonic wave dark matter ($psi$DM) is an emerging dark matter candidate contesting the conventional cold dark matter paradigm and a model subject to intense scrutiny of late. This work for the first time reports testable salient features pertinent to gravitational lenses of $psi$DM halos. $psi$DM halos are distinctly filled with large-amplitude, small-scale density fluctuations with $deltarho/rho_{rm halo}sim 1$ in form of density granules. This halo yields ubiquitous flux ratio anomalies of a few tens of percent, as is typically found for lensed quasars, and may also produce rare hexad and octad images, for sources located in well-defined caustic zones. We have found new critical features appearing in the highly de-magnified lens center when the halo has sufficiently high surface density near a very compact massive core.
We present multi-frequency VLA polarisation observations of nine gravitational lenses. The aim of these observations was to determine Faraday rotation measures (RM) for the individual lensed images, and to measure their continuum spectra over a wide range of frequencies.
Recent observations of galaxy luminosity profiles and dark matter simulations find luminosity and mass distributions characterized by central cusps rather than finite core radii. We introduce and implement a set of cusped ellipsoidal lens models which include limits similar to the Jaffe, Hernquist, eta and NFW models and apply them to the gravitational lenses APM 08279+5255 and B 1933+503. A successful model of APM 08279+5255 with its central, odd image requires a very shallow cusp, $gamma ltorder 0.4$ where $rho propto r^{-gamma}$ as $rto 0$, which is similar to a core rather than the favored $1 ltorder gamma ltorder 2$ cusps. B~1933+503, by contrast, is well modeled with a steep density cusp, $1.6 ltorder gamma ltorder 2.0$.
We present the optical spectra of four newly discovered gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried out using the Low Resolution Imaging Spectrograph on the W. M. Keck-I Telescope as part of a program to study galaxy-scale gravitational lenses. From our spectra we found the redshift of the background source in CLASS B0128+437 (z_s=3.1240+-0.0042) and the lensing galaxy redshifts in CLASS B0445+123 (z_l=0.5583+-0.0003) and CLASS B0850+054 (z_l=0.5883+-0.0006). Intriguingly, we also discovered that CLASS B0631+519 may have two lensing galaxies (z_l,1=0.0896+-0.0001, z_l,2=0.6196+-0.0004). We also found a single unidentified emission line from the lensing galaxy in CLASS B0128+437 and the lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS B0445+123 and CLASS B0631+519 (l,2) to be early-type galaxies with Einstein Radii of 2.8-3.0 h^{-1} kpc. The deflector in CLASS B0850+054 is a late-type galaxy with an Einstein Radius of 1.6 h^{-1} kpc.
We study in detail gravitational lensing caused by a supermassive fermion star and compare it with lensing by a black hole of the same mass. It is argued that lensing effects, being very distinct, may shed some light on the yet unexplained nature of the compact dark massive object at the Galactic center.