scholarly journals A simple simulation technique for gravitational lenses

2011 ◽  
Vol 20 (2) ◽  
pp. 183-189
Author(s):  
CRISTIAN EDUARD RUSU ◽  
◽  
BETRIA SILVANA ROSSA ◽  
Keyword(s):  
Present Article ◽  
Gravitational Lensing ◽  
Weak Field ◽  
Simulation Technique ◽  
Gravitational Lens ◽  
Gravitational Lenses ◽  
Direct Simulation ◽  
Single Plane ◽  
Advantages And Disadvantages ◽  
Simple Simulation

The present article discusses the simulation of Gravitational Lensing with an algorithm developed in C++ and using the EasyBMP library. The algorithm numerically solves the general gravitational lens equation in the astrophysically significant weak field case, for any single-plane lens configuration. Examples of execution are considered, and a discussion is carried out on the advantages and disadvantages of the direct simulation technique employed.

scholarly journals Gravitational Lensing

1992 ◽  
Vol 9 ◽  
pp. 3-32 ◽  
Author(s):  
Sjur Refsdal ◽  
Jean Surdej
Keyword(s):  
Gravitational Lensing ◽  
Gravitational Lens ◽  
Medium Size ◽  
Gravitational Lenses ◽  
Optical Lens ◽  
Basic Principles ◽  
History Of ◽  
Photometric Monitoring ◽  
A Site ◽  
Near Future

AbstractAtmospheric lensing effects deform our view of distant objects; similarly, without any doubt, gravitational lensing perturbs our view of the distant Universe and affects our physical understanding of various classes of extragalactic objects. We summarize here part of the theoretical and observational evidences supporting these claims.After briefly reviewing the history of gravitational lenses, we recall the basic principles underlying the formation of gravitationally lensed images of distant cosmic sources. We describe a simple optical lens experiment, which was actually shown during the oral discourse, and which accounts for all types of presently known gravitational lens systems.The various optical and radio searches for new gravitational lens systems that are being carried out at major observatories are reviewed. State-of-the-art observations of selected gravitational lens systems, obtained with highly performing ground-based telescopes, are then presented. These include several examples of multiply imaged QSO images, radio rings and giant luminous arcs.Through the modeling of these enigmatic objects, we show how it is possible to weigh the mass of distant lensing galaxies as well as to probe the distribution of luminous and dark matter in the Universe. Among the astrophysical and cosmological interests of observing and studying gravitational lenses, we also discuss the possibility of deriving the value of the Hubble parameter Ho from the measurement of a time delay, and how to determine the size and structure of distant quasars via the observational study of micro-lensing effects.At the end of this paper, we conclude on how to possibly achieve major astro-physical and cosmological goals in the near future by dedicating, on a site with good atmospheric seeing conditions, a medium size (2-3 m) telescope to the photometric monitoring of the multiple images of known and suspected gravitational lens systems.

GRAVITATIONAL LENS AMPLIFICATION OF GRAVITATIONAL RADIATION

2002 ◽  
Vol 11 (07) ◽  
pp. 1067-1074 ◽  
Author(s):  
ALEXANDER F. ZAKHAROV ◽  
YURI V. BARYSHEV
Keyword(s):  
Gravitational Wave ◽  
Gravitational Lensing ◽  
Gravitational Radiation ◽  
Gravitational Lens ◽  
Wave Form ◽  
Gravitational Lenses ◽  
Approximation Model ◽  
Radiation Sources ◽  
Wave Space ◽  
Stellar Masses

In a recent paper by Wang, Turner and Stebbins (1996) an influence of gravitational lensing on increasing an estimated rate of gravitational radiation sources was considered. We show that the authors used the geometrical optics approximation model for gravitational lensing and thus they gave overestimated rate of possible events for possible sources of gravitational radiation for the advanced LIGO detector. We show also that if we would use a more correct model of gravitational lensing, one could conclude that more strong influence on increasing rate of estimated events of gravitational radiation for advanced LIGO detector could give gravitational lenses of galactic masses but not gravitational lenses of stellar masses as Wang et al. concluced. Moreover, binary gravitational lenses could give essential distortion of gravitational wave form template, especially gravitational wave template of periodic sources and the effect could be significant for templates of quasi-periodic sources which could be detected by a future gravitational wave space detector like LISA.

scholarly journals A VLA Gravitational Lens Survey

1987 ◽  
Vol 124 ◽  
pp. 747-750
Author(s):  
J. N. Hewitt ◽  
E. L. Turner ◽  
B. F. Burke ◽  
C. R. Lawrence ◽  
C. L. Bennett ◽  
...  
Keyword(s):  
Dark Matter ◽  
Gravitational Field ◽  
Gravitational Lensing ◽  
Critical Density ◽  
Selection Effect ◽  
Compact Objects ◽  
Gravitational Lens ◽  
Gravitational Lenses ◽  
Number Density ◽  
Luminous Objects

Gravitational lens surveys are of cosmological interest because they provide a way to measure the gravitational field of both luminous and dark matter. Many of the other methods used to detect the presence of dark matter, such as studies of galaxy rotation curves and cluster dynamics, require that there be luminous objects in the gravitational field that act as tracers of the mass. This may introduce a selection effect. In constrast, in studies of gravitational lenses, the beacon we observe can be far (at distances of order one thousand Mpc) from the gravitational field. In this paper we describe a VLA survey designed to detect gravitational lensing on sub-arc second and arc second scales. We also present a preliminary result of the radio data: we find that the density of matter in the form of a uniform, comoving number density of 1011 to 1012M⊙ compact objects, luminous or dark, must be substantially less than the critical density.

scholarly journals Cosmological Applications of Gravitational Lensing

1996 ◽  
Vol 168 ◽  
pp. 209-217
Author(s):  
Peter Schneider
Keyword(s):  
Gravitational Lensing ◽  
High Redshift ◽  
Cosmological Parameters ◽  
Gravitational Lens ◽  
Mass Determination ◽  
Gravitational Lenses ◽  
Distant Object ◽  
The Many ◽  
The Universe

It was recognized very early that the gravitational lens effect can be used as an efficient cosmological tool. Of the many researchers who foresaw the use of lensing, F. Zwicky and S. Refsdal should be explicitly mentioned. The perhaps most accurate predictions and foresights by these two authors are as follows: Zwicky estimated the probability that a distant object is multiply imaged to be about 1/400, and thus that the observation of this effect is “a certainty” [73] – his value, which was obtained by a very crude reasoning, is in fact very close to current estimates of the lensing probability of high-redshift QSOs. He predicted that the magnification caused by gravitational light deflection will allow a “deeper look” into the universe –in fact, the spectroscopy of very faint galaxies which are imaged into giant luminous arcs have yielded spectral information which would be very difficult to obtain without these ‘natural telescopes’. And third, Zwicky saw that gravitational lenses may be used to determine the mass of distant extragalactic objects[72] – in fact, the mass determination of clusters masses from giant luminous arcs is as least as accurate as other methods, but does not rely on special assumptions (like spherical symmetry, virial or thermal equilibrium) inherent in other methods, and the determination of the mass within the inner 0.9 arcseconds of the lensing galaxy in the quadruple QSO 2237+0305 to within 2% [52] is the most accurate extragalactic mass determination known. Refsdal predicted the use of gravitational lenses for determining cosmological parameters and for testing cosmological theories [48][49] – we shall return to these issues below.

scholarly journals Quantifying the structure of strong gravitational lens potentials with uncertainty-aware deep neural networks

2020 ◽  
Vol 499 (4) ◽  
pp. 5641-5652
Author(s):  
Georgios Vernardos ◽  
Grigorios Tsagkatakis ◽  
Yannis Pantazis
Keyword(s):  
Confidence Intervals ◽  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Probability Distributions ◽  
Mass Density ◽  
Ground Truth ◽  
Gaussian Random Fields ◽  
Training Data ◽  
Gravitational Lens ◽  
Data Set

ABSTRACT Gravitational lensing is a powerful tool for constraining substructure in the mass distribution of galaxies, be it from the presence of dark matter sub-haloes or due to physical mechanisms affecting the baryons throughout galaxy evolution. Such substructure is hard to model and is either ignored by traditional, smooth modelling, approaches, or treated as well-localized massive perturbers. In this work, we propose a deep learning approach to quantify the statistical properties of such perturbations directly from images, where only the extended lensed source features within a mask are considered, without the need of any lens modelling. Our training data consist of mock lensed images assuming perturbing Gaussian Random Fields permeating the smooth overall lens potential, and, for the first time, using images of real galaxies as the lensed source. We employ a novel deep neural network that can handle arbitrary uncertainty intervals associated with the training data set labels as input, provides probability distributions as output, and adopts a composite loss function. The method succeeds not only in accurately estimating the actual parameter values, but also reduces the predicted confidence intervals by 10 per cent in an unsupervised manner, i.e. without having access to the actual ground truth values. Our results are invariant to the inherent degeneracy between mass perturbations in the lens and complex brightness profiles for the source. Hence, we can quantitatively and robustly quantify the smoothness of the mass density of thousands of lenses, including confidence intervals, and provide a consistent ranking for follow-up science.

scholarly journals Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen

1996 ◽  
Vol 173 ◽  
pp. 97-98
Author(s):  
Matthias Bartelmann ◽  
Abraham Loeb
Keyword(s):  
Observational Data ◽  
Gravitational Lensing ◽  
Column Density ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Absorption Lines ◽  
Gravitational Lenses ◽  
High Column

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.

scholarly journals When Darwin Met Einstein: Gravitational Lens Inversion with Genetic Algorithms

2005 ◽  
Vol 22 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Brendon J. Brewer ◽  
Geraint F. Lewis
Keyword(s):  
Genetic Algorithms ◽  
Gravitational Lensing ◽  
Surface Brightness ◽  
Initial Study ◽  
Brightness Distribution ◽  
Gravitational Lens ◽  
Atmospheric Effects ◽  
Lens Model ◽  
New Approach ◽  
Genetic Algorithm Approach

AbstractGravitational lensing can magnify a distant source, revealing structural detail which is normally unresolvable. Recovering this detail through an inversion of the influence of gravitational lensing, however, requires optimisation of not only lens parameters, but also of the surface brightness distribution of the source. This paper outlines a new approach to this inversion, utilising genetic algorithms to reconstruct the source profile. In this initial study, the effects of image degradation due to instrumental and atmospheric effects are neglected and it is assumed that the lens model is accurately known, but the genetic algorithm approach can be incorporated into more general optimisation techniques, allowing the optimisation of both the parameters for a lensing model and the surface brightness of the source.

AN APPLICATION OF THE TOPOLOGICAL DEGREE TO GRAVITATIONAL LENSES

1998 ◽  
Vol 13 (02) ◽  
pp. 83-86 ◽  
Author(s):  
MARCO LOMBARDI
Keyword(s):  
Point Source ◽  
Mass Distribution ◽  
Topological Degree ◽  
General Theorem ◽  
Gravitational Lens ◽  
Gravitational Lenses ◽  
General Proof ◽  
Special Case

In this letter we provide a new proof of a general theorem on gravitational lenses, first proven by Burke (1981) for the special case of thin lenses. The theorem states that a transparent gravitational lens with non-singular mass distribution produces an odd number of images of a point source. Our general proof shows that the topological degree finds natural and interesting applications in the theory of gravitational lenses.

scholarly journals APPROACH TO RATIONAL CALCULATION OF SUPERELEVATION IN DUAL GAUGE TRACK

Transport ◽  
2018 ◽  
Vol 33 (3) ◽  
pp. 699-706 ◽  
Author(s):  
Inesa Gailienė ◽  
Martynas Gedaminskas ◽  
Alfredas Laurinavičius
Keyword(s):  
Present Article ◽  
Geometrical Parameter ◽  
Advantages And Disadvantages ◽  
Rail Wear ◽  
Calculation Methodology ◽  
Rational Calculation ◽  
The Subject

One of the technical possibilities to solve a gauge crossing is to install a dual gauge. This solution has several advantages and disadvantages discussed in this paper. Lack of experience of maintenance and lack of standards for the design of dual track are among the most important disadvantages. The wheel and rail interface on track curves is more difficult than in straight sections. Therefore, the subject of the present article is a geometrical parameter of dual gauge track, i.e., the rail superelevation, which has an impact on the wheel–rail interaction at curves and influences the value of uncompensated acceleration, occurring when a train passes a curve, and, consequently, the intensity of rail wear. The objective of the present article is to analyse the features of dual gauge track and the superelevation calculation methodology considered, to present the approach to rational calculation of superelevation for dual gauge track of Šeštokai–Mockava (Lithuania–Poland) using several calculation versions as well as to make recommendations for the calculation of superelevation.

scholarly journals Weak Deflection Angle of some Classes of non-linear Electrodynamics Black Holes via Gauss-Bonnet Theorem

2020 ◽  
Author(s):  
Hasan El Moumni ◽  
Karima Masmar ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Weak Field ◽  
Leading Order ◽  
Plasma Medium ◽  
Non Linear ◽  
The Deflection Angle ◽  
Bonnet Theorem

In this paper, we study the gravitational lensing by some black hole classes within the non-linear electrodynamics in weak field limits. First, we calculate an optical geometry of the non-linear electrodynamics black hole then we use the Gauss-Bonnet theorem for finding deflection angle in weak field limits. The effect of non-linear electrodynamics on the deflection angle in leading order terms is studied. Furthermore, we discuss the effects of the plasma medium on the weak deflection angle.

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