Einstein ring

Abstract: Almost all stars are in binary systems. When the separation between the two components is comparable to the Einstein ring radius corresponding to the combined mass of the binary acting as a gravitational lens, then an extra pair of images can be created, and the light curve of a lensed source becomes complicated. It is estimated that about 10 percent of all lensing episodes of the Galactic bulge stars will strongly display the binary nature of the lens. The effect is strong even if the companion is a planet. A massive search for microlensing of the Galactic bulge stars may lead to a discovery of the first extrasolar planetary systems.

Abstract: Using backwards ray tracing, we study the shadows of Kerr black holes with scalar hair (KBHSH). KBHSH interpolate continuously between Kerr BHs and boson stars (BSs), so we start by investigating the lensing of light due to BSs. Moving from the weak to the strong gravity region, BSs-which by themselves have no shadows-are classified, according to the lensing produced, as (i) noncompact, which yield not multiple images, (ii) compact, which produce an increasing number of Einstein rings and multiple images of the whole celestial sphere, and (iii) ultracompact, which possess light rings, yielding an infinite number of images with (we conjecture) a self-similar structure. The shadows of KBHSH, for Kerr-like horizons and noncompact BS-like hair, are analogous to, but distinguishable from, those of comparable Kerr BHs. But for non-Kerr-like horizons and ultracompact BS-like hair, the shadows of KBHSH are drastically different: novel shapes arise, sizes are considerably smaller, and multiple shadows of a single BH become possible. Thus, KBHSH provide quantitatively and qualitatively new templates for ongoing (and future) very large baseline interferometry observations of BH shadows, such as those of the Event Horizon Telescope.

Abstract: We present the definitive data for the full sample of 131 strong gravitational lens candidates observed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope by the Sloan Lens ACS (SLACS) Survey. All targets were selected for higher redshift emission lines and lower redshift continuum in a single Sloan Digital Sky Survey (SDSS) spectrum. The foreground galaxies are primarily of early-type morphology, with redshifts from z similar or equal to 0.05 to 0.5 and velocity dispersions from sigma similar or equal to 160 to 400 km s(-1); the faint background emission-line galaxies have redshifts ranging from z similar or equal to 0.2 to 1.2. We confirm 70 systems showing clear evidence of multiple imaging of the background galaxy by the foreground galaxy, as well as an additional 19 systems with probable multiple imaging. For 63 clear lensing systems, we present singular isothermal ellipsoid and light-traces-mass gravitational lens models fitted to the ACS imaging data. These strong-lensing mass measurements are supplemented by magnitudes and effective radii measured from ACS surface brightness photometry and redshifts and velocity dispersions measured from SDSS spectroscopy. These data constitute a unique resource for the quantitative study of the interrelations between mass, light, and kinematics in massive early-type galaxies. We show that the SLACS lens sample is statistically consistent with being drawn at random from a parent sample of SDSS galaxies with comparable spectroscopic parameters and effective radii, suggesting that the results of SLACS analyses can be generalized to the massive early-type population.

Abstract: We report the detection of a dark substructure - undetected in the Hubble Space Telescope HST ACS F814W image -in the gravitational lens galaxy SDSSJ0946+1006 (the 'double Einstein ring'), through direct gravitational imaging. The detection of a small mass concentration in the surface density maps, at 4.3 kpc from the galaxy centre, has a strong statistical significance. We confirm this detection by modelling the substructure with a tidally truncated pseudo-Jaffe density profile; in that case the substructure mass is M(sub) = (3.51 +/- 0.15) x 10(9) M(circle dot), precisely where also the surface density map shows a strong convergence peak (Bayes factor Delta log epsilon = -128.0; equivalent to a similar to 16 sigma detection). The result is robust under substantial changes in the model. We set a lower limit of (M/L)(V,circle dot) greater than or similar to 120 M(circle dot)/L(V,circle dot) (3 sigma) inside a sphere of 0.3 kpc centred on the substructure (r(tidal) = 1.1 kpc). The mass and luminosity limit of this substructure are consistent with Local Group results if the substructure had a virial mass of similar to 10(10) M(circle dot) before accretion and formed at z greater than or similar to 10. Our detection implies a projected dark matter mass fraction in substructure at the radius of the inner Einstein ring of f = 2.15(-1.25)(+2.05) per cent [68 per cent confidence level (CL)] in the mass range 4 x 10(6)-4 x 10(9) M(circle dot), assuming alpha = 1.9 +/- 0.1 (with dN/dm alpha m(-alpha)). Assuming a flat prior on alpha, between 1.0 and 3.0, increases this to f = 2.56(-1.50)(+3.26) per cent (68 per cent CL). The likelihood ratio is similar to 0.5 between these fractions and that from simulations (f(N-body) approximate to 0.003). Hence the inferred dark matter mass fraction in substructure, admittedly based on a single-lens system, is large but still consistent with predictions.