Quadruple Lens System Research Articles

Electrostatic focusing lens system for low MeV-ion microprobe: A simulation and optimization study

In this work, we studied and optimized the performance of electrostatic quadruple focusing lens system. Combining the power of three simulation software, we explored the lens hyper-parameter space to maximize the Figure of Merit Q that is proportional to the magnitude of the product of the horizontal and vertical demagnifications and inversely proportional to the product of the spherical aberration coefficients. For a 3 MeV/q beam with beam emittance of 0.2 μm·mrad, the most compact and high-performance system we obtained was an electrostatic quadruple triplet (EQT), which had a Q value of 24 and a length of ∼0.5 m, measured from the divergence slit to the end of the last set of electrodes. Increasing the distance l between the divergence aperture and the first lens further increased the Q value. l=1.0 m seems to be a good trade-off between maximizing the Q value and minimizing the system length, under which Q was approximately 33.

Gravitational Lens System PS J0147+4630 (Andromeda’s Parachute): Main Lensing Galaxy and Optical Variability of the Quasar Images

Abstract Because follow–up observations of quadruple gravitational lens systems are of extraordinary importance for astrophysics and cosmology, we present single-epoch optical spectra and r-band light curves of PS J0147+4630. This recently discovered system mainly consists of four images ABCD of a background quasar around a foreground galaxy G that acts as a gravitational lens. First, we use long-slit spectroscopic data in the Gemini Observatory Archive and a multi-component fitting to accurately resolve the spectra of A, D, and G. The spectral profile of G resembles that of an early-type galaxy at a redshift of 0.678 ± 0.001, which is about 20% higher than the previous estimate. Additionally, the stellar velocity dispersion is measured to ∼5% precision. Second, our early r-band monitoring with the Liverpool Telescope leads to accurate light curves of the four quasar images. Adopting time delays predicted by the lens model, the new lens redshift, and a standard cosmology, we report the detection of microlensing variations in C and D as large as ∼0.1 mag on timescales of a few hundred days. We also estimate an actual delay between A and B of a few days (B is leading), which demonstrates the big potential of optical monitoring campaigns of PS J0147+4630.

On the origin of the flux ratio anomaly in quadruple lens systems

We explore the origin of flux ratio anomaly in quadruple lens systems. Using a semi-analytic method based on $N$-body simulations, we estimate the effect of possible magnification perturbation caused by subhaloes with a mass scale of <$\sim 10^9\,h^{-1} \textrm{M}_\odot$ in lensing galaxy haloes. Taking into account astrometric shifts, assuming that the primary lens is described by a singular isothermal ellipsoid, the expected change to the flux ratios per a multiply lensed image is just a few percent and the mean of the expected convergence perturbation at the effective Einstein radius of the lensing galaxy halo is $ 0.003$, corresponding to the mean of the ratio of a projected dark matter mass fraction in subhaloes at the effective Einstein radius $0.006$. In contrast, the expected change to the flux ratio caused by line-of-sight structures is typically $\sim 10$ percent and the mean of the convergence perturbation is $0.008$, corresponding to $0.017$. The contribution of magnification perturbation caused by subhaloes is $\sim 40$ percent of the total at a source redshift $z_S= 0.7$ and decreases monotonically in $z_S$ to $\sim 20$ percent at $z_S= 3.6$. Assuming statistical isotropy, the convergence perturbation estimated from observed 11 quadruple lens systems has a positive correlation with the source redshift $z_S$, which is much stronger than that with the lens redshift $z_L$. This feature also supports an idea that the flux ratio anomaly is caused mainly by line-of-sight structures rather than subhaloes. We also discuss about a possible imprint of line-of-sight structures in demagnification of minimum images due to locally underdense structures in the line of sight.

Time-delay cosmography: increased leverage with angular diameter distances

Strong lensing time-delay systems constrain cosmological parameters via the so-called time-delay distance and the angular diameter distance to the lens. In previous studies, only the former information was used in forecasting cosmographic constraints. In this paper, we show that the cosmological constraints improve significantly when the latter information is also included. Specifically, the angular diameter distance plays a crucial role in breaking the degeneracy between the curvature of the Universe and the time-varying equation of state of dark energy. Using a mock sample of 55 bright quadruple lens systems based on expectations for ongoing/future imaging surveys, we find that adding the angular diameter distance information to the time-delay distance information and the Planck's measurements of the cosmic microwave background anisotropies improves the constraint on the constant equation of state by 30%, on the time variation in the equation of state by a factor of two, and on the Hubble constant in the flat ΛCDM model by a factor of two. Therefore, previous forecasts for the statistical power of time-delay systems were overly pessimistic, i.e., time-delay systems are more powerful than previously appreciated.

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

We investigate the weak lensing effect by line-of-sight structures with a surface mass density of <~10^8 solar mass/arcsec^2 in QSO-galaxy quadruple lens systems. Using high-resolution N-body simulations in warm dark matter (WDM) models and observed four quadruple lenses that show anomalies in the flux ratios, we obtain constraints on the mass of thermal WDM, m_WDM>= 1.3keV(95%CL) assuming that the density of the primary lens is described by a singular isothermal ellipsoid (SIE). The obtained constraint is consistent with those from Lyman-$\alpha$ forests and the number counts of high-redshift galaxies at z>4. Our results show that WDM with a free-streaming comoving wavenumber k_{fs} <= 27 h/Mpc is disfavored as the major component of cosmological density at redshifts 0.5 <~ z <~ 4 provided that the SIE models describe the gravitational potentials of the primary lenses correctly.

Weak lensing by intergalactic ministructures in quadruple lens systems: simulation and detection

We investigate the weak lensing effects of line-of-sight structures on quadruple images in quasar-galaxy strong lens systems based on N-body and ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass. The intervening halos and voids disturb the magnification ratios of lensed images as well as their relative positions due to lensing. The magnification ratios typically change by O(10%) when the shifts of relative angular positions of lensed images are constrained to <0.004 arcsec. The constrained amplitudes of projected density perturbations due to line-of-sight structures are O(10^8) solar mass per arcsec^2. These results are consistent with our new analytical estimate based on the two-point correlation of density fluctuations. The observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with quadruple images agree well with the numerically estimated values without taking into account of subhalos residing in the lensing galaxies. We find that the constrained mean amplitudes of projected density perturbations in the line-of-sight are negative, which suggests that the fluxes of lensed images are perturbed mainly by minivoids and minihalos in underdense regions. We derive a new fitting formula for estimating the probability distribution function of magnification perturbation. We also find that the mean amplitude of magnification perturbation roughly equals the standard deviation regardless of the model parameters.

THE STRUCTURE OF THE X-RAY AND OPTICAL EMITTING REGIONS OF THE LENSED QUASAR Q 2237+0305

We use gravitational microlensing to determine the size of the X-ray and optical emission regions of the quadruple lens system Q 2237+0305. The optical half-light radius, log(R_{1/2,V}/cm)=16.41\pm0.18 (at lambda_{rest}=2018 \AA), is significantly larger than the observed soft, log(R_{1/2,soft}/cm)=15.76^{+0.41}_{-0.34} (1.1-3.5 keV in the rest frame), and hard, log(R_{1/2,hard}/cm)=15.46^{+0.34}_{-0.29} (3.5-21.5 keV in the rest frame), band X-ray emission. There is a weak evidence that the hard component is more compact than the soft, with log(R_{1/2,soft}/R_{1/2,hard}) \sim 0.30^{+0.53}_{-0.45}. This wavelength-dependent structure agrees with recent results found in other lens systems using microlensing techniques, and favors geometries in which the corona is concentrated near the inner edge of the accretion disk. While the available measurements are limited, the size of the X-ray emission region appears to be roughly proportional to the mass of the central black hole.

FOLD LENS FLUX ANOMALIES: A GEOMETRIC APPROACH

We develop a new approach for studying flux anomalies in quadruply imaged fold lens systems. We show that in the absence of substructure, microlensing, or differential absorption, the expected flux ratios of a fold pair can be tightly constrained using only geometric arguments. We apply this technique to 11 known quadruple lens systems in the radio and infrared and compare our estimates to the Monte Carlo based results of Keeton et al. We show that a robust estimate for a flux ratio from a smoothly varying potential can be found, and at long wavelengths those lenses deviating from this ratio almost certainly contain significant substructure.

SUBARU MID-INFRARED IMAGING OF THE QUADRUPLE LENSES. II. UNVEILING LENS STRUCTURE OF MG0414+0534 AND Q2237+030

We present mid-infrared imaging at 11.7 $\mu$m for the quadruple lens systems, MG0414+0534 and Q2237+030, using the cooled mid-infrared camera and spectrometer (COMICS) attached on the Subaru telescope. MG0414+0534 is characterized by a bright pair of lensed images (A1, A2) and their optical flux ratio A2/A1 deviates significantly from the prediction of a smooth lens model. Q2237+030 is comprised of four lensed images, which are significantly affected by microlensing in a foreground lensing galaxy. Our mid-infrared observations of these lensed images have revealed that the mid-infrared flux ratio for A2/A1 of MG0414+0534 is nearly unity (0.90 +- 0.04). We find that this flux ratio is systematically small, at 4 to 5 sigma level, compared with the prediction of a best smooth lens model (1.09) represented by a singular isothermal ellipsoid and external shear, thereby suggesting the presence of substructures to explain our observational result. In contrast, for Q2237+030, our high signal-to-noise observation indicates that the mid-infrared flux ratios between all the four images of Q2237+030 are virtually consistent with the prediction of a smooth lens model. Based on the size estimate of the dust torus surrounding the nuclei of these QSOs, we set limits on the mass of a substructure in these lens systems, which can cause anomalies in the flux ratios. For MG0414+0534, since the required mass of a substructure inside its Einstein radius is > 360 M_sun, millilensing by a CDM substructure is most likely. If it is modeled as a singular isothermal sphere, the mass inside radius of 100 pc is given as > 1.0x10^5 M_sun. For Q2237+030, there is no significant evidence of millilensing, so the reported anomalous flux ratios in shorter wavelengths are entirely caused by microlensing by stars (abridged).

Q2237+0305 in X-rays: spectra and variability with XMM-Newton

Aims. X-ray observations of gravitationally lensed quasars may allow us to probe the inner structure of the central engine of a quasar. Observations of Q2237+0305 (Einstein Cross) in X-rays may be used to constrain the inner structure of the X-ray emitting source. Methods. Here we analyze the XMM-Newton observation of the quasar in the gravitational lens system Q2237+0305 taken during 2002. Combined spectra of the four images of the quasar in this system were extracted and modelled with a power-law model. Statistical analysis was used to test the variability of the total flux. Results. The total X-ray flux from all the images of this quadruple gravitational lens system is 6 × 10 −13 erg/(cm 2 s) in the range 0.2–10 keV, showing no significant X-ray spectral variability during almost 42 ks of the observation time. Fitting of the cleaned source spectrum yields a photon power-law index of Γ= 1.82 +0.07 −0.08 . The X-ray lightcurves obtained after background subtraction are compatible with the hypothesis of a stationary flux from the source.

High-resolution imaging of the anomalous flux ratio gravitational lens system CLASS B2045+265: dark or luminous satellites?

The existence of flux ratio anomalies between fold and cusp images in galaxy-scale strong-lens systems has led to an interpretation based on the presence of a high mass fraction of cold dark matter (CDM) substructures around galaxies, as predicted by numerical N-body simulations. These substructures can cause large perturbations of the image magnifications, leading to changes in the image flux ratios. The flux ratio anomaly is particularly evident in the radio-loud quadruple gravitational lens system CLASS B2045+265. In this paper, new high-resolution radio, optical and infrared imaging of B2045+265 is presented which sheds more light on this anomaly and its possible causes. First, deep Very Long Baseline Array observations show very compact images, possibly with a hint of a jet, but with no evidence for differential scattering or scatter broadening. Hence, the flux ratio anomaly is unlikely to be caused by refractive scattering in either the Milky Way or the lens galaxy. Secondly, optical and infrared observations with the Hubble Space Telescope and through adaptive optics imaging with the W. M. Keck Telescope, show a previously undiscovered object - interpreted as a (tidally disrupted) dwarf satellite based on its colours and slight extension - between the main lens galaxy and the three anomalous flux ratio images. Thirdly, colour variations in the early-type lens galaxy indicate recent star formation, possibly the result of secondary infall of gas-rich satellites. A population of such galaxies around the lens system could explain the previously discovered strong [O II] emission. However, spiral structure and/or normal star formation in the lens galaxy cannot be excluded. In light of these new data, we propose a lens model for the system, including the observed dwarf satellite, which reproduces all positional and flux ratio constraints, without the need for additional CDM substructure. Although the model is peculiar in that the dwarf galaxy must be highly flattened, the model is very similar to recently proposed mass models based on high-order multipole expansions.

Subaru Mid‐Infrared Imaging of the Quadruple Lenses PG 1115+080 and B1422+231: Limits on Substructure Lensing

We present mid-infrared imaging at 11.7 μm for the quadruple lens systems PG 1115+080 and B1422+231 using the cooled mid-infrared camera and spectrometer (COMICS) attached on the Subaru Telescope. These lensed QSOs are characterized by their anomalous optical and radio flux ratios, as obtained for A1 and A2 images of PG 1115+080 and A, B, and C images of B1422+231, respectively, i.e., such flux ratios are hardly able to be reproduced by lens models with a smooth mass distribution. Our mid-infrared observations for these images have revealed that the mid-infrared flux ratio A2/A1 of PG 1115+080 is virtually consistent with smooth lens models (but inconsistent with the optical flux ratio), whereas for B1422+231, the mid-infrared flux ratios among the A, B, and C images are in good agreement with the radio flux ratios. We also identify a clear infrared bump in the spectral energy distributions of these QSOs, thereby indicating that the observed mid-infrared fluxes originate from a hot dust torus around a QSO nucleus. Based on the size estimate of the dust torus, we place limits on the mass of a substructure in these lens systems causing the anomalous optical or radio flux ratios. For PG 1115+080, the mass of a substructure inside an Einstein radius ME is 16 M☉, corresponding to either a star or a low-mass CDM subhalo having a mass of M 2.2 × 104 M☉ inside a radius of 100 pc if modeled as a singular isothermal sphere (SIS). For B1422+231, we obtain ME 209 M☉, indicating that a CDM subhalo is more likely, having a mass of M 7.4 × 104 M☉.

Galaxy Structures and External Perturbations in Gravitational Lenses

Abstract In modeling strong gravitational lens systems, one often adopts simple models, such as singular isothermal elliptical density plus lowest-order external perturbation. However, such simple models may mislead us if the real mass distribution is more complicated than that in the assumed models. In particular, assumptions on mass models are crucial in studying flux ratio anomalies that have been suggested as evidence for a cold dark-matter substructure. We reinvestigated four quadruple lens systems using power-law Fourier models, which have advantages of clear physical meanings and the applicability of a linear method, as well as a simple singular isothermal elliptical density model. We also investigated the effect of external perturbations, including a singular isothermal sphere, lowest-order expansion, and next-order expansion. We have found that the $\cos 3\theta$ terms of the primary galaxy and/or of external perturbation significantly reduce the $\chi^2$ in PG 1115$+$080 and B1422$+$231. In particular, we could reproduce the flux ratios of B1422$+$231 with next-order external perturbation assuming 5% flux uncertainties, suggesting that external perturbation cannot be described by a simple singular isothermal sphere approximation. On the other hand, we could not fit B0712$+$472 and B2045$+$265 very well even with our models, although the $\chi^2$ were reduced compared with the case of using simple models. Our results clearly demonstrate that both the primary lens galaxy and the external perturbation are often more complicated than we usually assume.

Science verification results from PMAS

AbstractPMAS, the Potsdam Multi‐Aperture Spectrophotometer, is a new integral field instrument which was commissioned at the Calar Alto 3.5 m Telescope in May 2001. We report on results obtained from a science verification run in October 2001. We present observations of the low‐metallicity blue compact dwarf galaxy SBS0335‐052, the ultra‐luminous X‐ray Source X‐1 in the Holmberg II galaxy, the quadruple gravitational lens system Q2237+0305 (the “Einstein Cross”), the Galactic planetary nebula NGC7027, and extragalactic planetary nebulae in M31. PMAS is now available as a common user instrument at Calar Alto Observatory. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Microlensing-induced spectral variability in Q 2237 + 0305

We present both photometry and spectra of the individual images of the quadruple gravitational lens system Q2237+0305. Comparison of spectra obtained at two epochs, separated by $\sim~3\,$years, shows evidence for significant changes in the emission line to continuum ratio of the strong ultraviolet CIV~$\lambda$1549, CIII]~$\lambda$1909 and MgII~$\lambda$2798 lines. The short, $\sim~1\,$day, light--travel time differences between the sight lines to the four individual quasar images rule out any explanation based on intrinsic variability of the source. The spectroscopic differences thus represent direct detection of microlensing--induced spectroscopic differences in a quasar. The observations allow constraints to be placed on the relative spatial scales in the nucleus of the quasar, with the ultra--violet continuum arising in a region of $\la~0.05~{\rm pc}$ in extent, while the broad emission line material is distributed on scales much greater than this.

Using Quadruple Lenses to Probe the Structure of the Lensing Galaxy

We show here that quadruple lenses can be useful laboratories to probe whether the potential of the lensing galaxy is purely elliptical or whether an additional distortion is present in the deflector plane. For this test we only have to know the relative image positions of the quadruple lens system and the (relative) center of light position of the lensing galaxy. Furthermore, we introduce new methods that easily allow us to determine the location (rotation angle relative to the image positions) of the major axis of the lensing galaxy. In due course, we can determine the parity of the four images as well. We apply these methods to the eight currently known quadruple lenses and find that in the case of MG 0414+0534, CLASS 1608+656, and HST 12531-2914 it is impossible to accommodate the relative image positions and the galaxy position with any elliptical potential, whereas the other five cases can be described very well with a simple elliptical potential. This method will have important impacts for χ2 fits and the reconstruction of galaxy models for quadruple lenses.

The Variability Of PG1115+080

PG1115+080 (Weymann et al. 1980), the first quadruple lens system, remains the most promising for an optical measurement of the Hubble constant through a time delay. Factors contributing to this assessment include the well constrained geometry, the apparent magnitudes of the four components (Christian et al. 1987), the expected time delay (Narasimha &amp; Chitre 1992), and the position of the lensing galaxy (Kristian et al. 1993). There are nonetheless many factors which combine to render this a difficult measurement, among them the small separation of the images and the small variability amplitude and long variability time scale of the “typical” optically selected quasar (Hook et al 1994). The measurement is further complicated by the likelihood of microlensing of the individual components (Witt et al. 1995), which depends upon the degree to which the quasar is resolved and the fraction of the lens mass in microlenses.

Parameter degeneracy in models of the quadruple lens system Q2237+0305

The geometry of the quadruple lens system Q2237+0305 is modeled with a simple astigmatic lens: a power-law mass distribution: m approximately r(exp beta) with an external shear gamma. The image positions can be reproduced with an accuracy better than 0.01 arcsec for any 0.0 less than or = beta less than or = 1.85 and the corresponding value of gamma = 0.1385-0.0689 beta. This is a factor of approximately 4 more precise than what can be achieved by the best constant stellar mass/L lens models. The image intensity ratios and the time delay ratios are almost constant along our one parameter family of models, but the total magnification varies from 8 to greater than 1000, and the maximum time delay (between leading image B and trailing image C) for H(sub 0) of 75 km/s (Mpc) varies from more than 20 h to about 1.5 h, while beta increases from 0.0 to 1.85.

The central velocity dispersion of the lensing galaxy in the quadruple lens system Q2237 + 0305

view Abstract Citations (37) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Central Velocity Dispersion of the Lensing Galaxy in the Quadruple Lens System Q2237+0305 Foltz, Craig B. ; Hewett, Paul C. ; Webster, Rachel L. ; Lewis, Geraint F. Abstract We report a measurement of the projected central velocity dispersion for the lensing galaxy in the quadruple gravitational lens system Q2237 + 0305. Observations of the galaxy nucleus taken in superb Seeing conditions with the 4.2 m William Herschel Telescope produce a value for the central velocity dispersion of σ_p_= 215 +/- 30 km s^-1^. The value is consistent with the predictions of theoretical models of the lensing galaxy's mass distribution, but the measurement suggests there is evidence for some degree of anisotropy in the velocity dispersion of the galaxy bulge. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/186288 Bibcode: 1992ApJ...386L..43F Keywords: Gravitational Lenses; Spiral Galaxies; Velocity Distribution; Astronomical Spectroscopy; Charge Coupled Devices; Galactic Bulge; Galactic Nuclei; Telescopes; Astrophysics; COSMOLOGY: GRAVITATIONAL LENSING; GALAXIES: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (5) NED (5)