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ABSTRACT: The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy
lensing a background quasar into two bright images. Previous efforts to
constrain the mass distribution in the galaxy have suggested that at least one
additional image must be present (Castander et al. 2006). These extra images
may be hidden behind the disk which features a prominent dust lane. We present
and analyze Hubble Space Telescope (HST) observations of the system. We do not
detect any extra images, but the observations further narrow the observable
parameters of the lens system. We explore a range of models to describe the
mass distribution in the system and find that a variety of acceptable model
fits exist. All plausible models require 2 magnitudes of dust extinction in
order to obscure extra images from detection, and some models may require an
offset between the center of the galaxy and the center of the dark matter halo
of 1 kiloparsec. Currently unobserved images will be detectable by future James
Webb Space Telescope (JWST) observations and will provide strict constraints on
the fraction of mass in the disk.
11/2012;
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ABSTRACT: We present a microlensing analysis of 61 Chandra observations of 14 quadruply
lensed quasars. X-ray flux measurements of the individual quasar images give a
clean determination of the microlensing effects in the lensing galaxy and thus
offer a direct assessment of the local fraction of stellar matter making up the
total integrated mass along the lines of sight through the lensing galaxy. A
Bayesian analysis of the ensemble of lensing galaxies gives a most likely local
stellar fraction of 7%, with the other 93% in a smooth, dark matter component,
at an average impact parameter R_c of 6.6 kpc from the center of the lensing
galaxy. We divide the systems into smaller ensembles based on R_c and find that
the most likely local stellar fraction varies qualitatively and quantitatively
as expected, decreasing as a function of R_c.
08/2011;
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ABSTRACT: Microlensing perturbations to the flux ratios of gravitationally lensed
quasar images can vary with wavelength because of the chromatic dependence of
the accretion disk's apparent size. Multiwavelength observations of microlensed
quasars can thus constrain the temperature profiles of their accretion disks, a
fundamental test of an important astrophysical process which is not currently
possible using any other method. We present single-epoch broadband flux ratios
for 12 quadruply lensed quasars in eight bands ranging from 0.36 to 2.2
microns, as well as Chandra 0.5--8 keV flux ratios for five of them. We combine
the optical/IR and X-ray ratios, together with X-ray ratios from the
literature, using a Bayesian approach to constrain the half-light radii of the
quasars in each filter. Comparing the overall disk sizes and wavelength slopes
to those predicted by the standard thin accretion disk model, we find that on
average the disks are larger than predicted by nearly an order of magnitude,
with sizes that grow with wavelength with an average slope of ~0.2 rather than
the slope of 4/3 predicted by the standard thin disk theory. Though the error
bars on the slope are large for individual quasars, the large sample size lends
weight to the overall result. Our results present severe difficulties for a
standard thin accretion disk as the main source of UV/optical radiation from
quasars.
07/2010;
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Paul L. Schechter,
Charles D. Bailyn,
Robert Barr,
Richard Barvainis,
Christopher M. Becker,
Gary M. Bernstein,
John P. Blakeslee,
Schelte J. Bus,
Alan Dressler,
Emilio E. Falco, [......],
Andreas O. Jaunsen,
Mario Mateo,
Doerte Mehlert,
Douglas O. Richstone,
Linda S. Sparke,
John R. Thorstensen,
John L. Tonry,
Gary Wegner,
Daryl W. Willmarth,
and Guy Worthey
[show abstract]
[hide abstract]
ABSTRACT: Optical photometry is presented for the quadruple gravitational lens PG 1115+080. A preliminary reduction of data taken from 1995 November to 1996 June gives component C leading component B by 23.7 ± 3.4 days and components A1 and A2 by 9.4 days. A range of models has been fitted to the image positions, none of which gives an adequate fit. The best-fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km s-1 Mpc-1 for Ω = 1, with an observational uncertainty of 14%, as computed from the B - C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0 = 64 km s-1 Mpc-1, while taking the galaxy to be a point mass gives H0 = 84 km s-1 Mpc-1. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned Hubble Space Telescope observations.
The Astrophysical Journal 01/2009; 475(2):L85. · 6.02 Impact Factor
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ABSTRACT: When a gravitationally lensed source crosses a caustic, a pair of images is created or destroyed. We calculate the mean number of such pairs of microimages n for a given macroimage of a gravitationally lensed point source due to microlensing by the stars of the lensing galaxy. This quantity was calculated by Wambsganss, Witt, and Schneider in 1992 for the case of zero external shear, γ = 0, at the location of the macroimage. Since in realistic lens models a nonzero shear is expected to be induced by the lensing galaxy, we extend this calculation to a general value of γ. We find a complex behavior of n as a function of γ and the normalized surface mass density in stars, κ*. Specifically, we find that at high magnifications, where the average total magnification of the macroimage is μ = |(1 - κ*)2 - γ2|-1 1, n becomes correspondingly large and is proportional to μ. The ratio n/μ is largest near the line γ = 1 - κ*, where the magnification μ becomes infinite, and its maximal value is 0.306. We compare our semianalytic results for n with the results of numerical simulations and find good agreement. We find that the probability distribution for the number of extra microimage pairs is reasonably described by a Poisson distribution with a mean value of n and that the width of the macroimage magnification distribution tends to be largest for n ~ 1.
The Astrophysical Journal 12/2008; 583(2):575. · 6.02 Impact Factor
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ABSTRACT: A "friends-of-friends" percolation algorithm has been used to extract a catalog of δn/n = 80 density enhancements (groups) from the six slices of the Las Campanas Redshift Survey (LCRS). The full catalog contains 1495 groups and includes 35% of the LCRS galaxy sample. A clean sample of 394 groups has been derived by culling groups from the full sample that either are too close to a slice edge, have a crossing time greater than a Hubble time, have a corrected velocity dispersion of zero, or contain a 55'' "orphan" (a galaxy with a mock redshift that was excluded from the original LCRS redshift catalog due to its proximity to another galaxy—i.e., within 55''). Median properties derived from the clean sample include a line-of-sight velocity dispersion σlos = 164 km s-1, crossing time tcr = 0.10 H, harmonic radius Rh = 0.58 h-1 Mpc, pairwise separation Rp = 0.64 h-1 Mpc, virial mass Mvir = 1.90 × 1013 h-1 M, total group R-band luminosity Ltot = 1.30 × 1011 h-2 L, and R-band mass-to-light ratio M/L = 171 h M/L; the median number of observed members in a group is three.
The Astrophysical Journal Supplement Series 12/2008; 130(2):237. · 13.46 Impact Factor
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Jens Hjorth,
Ingunn Burud,
Andreas O. Jaunsen, Paul L. Schechter,
Jean-Paul Kneib,
Michael I. Andersen,
Heidi Korhonen,
Jacob W. Clasen,
A. Amanda Kaas,
Roy Østensen,
Jaan Pelt,
and Frank P. Pijpers
[show abstract]
[hide abstract]
ABSTRACT: We present optical light curves of the gravitationally lensed components A (≡A1+A2+A3) and B of the quadruple quasar RX J0911.4+0551 (z = 2.80). The observations were primarily obtained at the Nordic Optical Telescope between 1997 March and 2001 April and consist of 74 I-band data points for each component. The data allow the measurement of a time delay of 146 ± 8 days (2 σ) between A and B, with B as the leading component. This value is significantly shorter than that predicted from simple models and indicates a very large external shear. Mass models including the main lens galaxy and the surrounding massive cluster of galaxies at z = 0.77, responsible for the external shear, yield H0 = 71 ± 4 (random, 2 σ) ± 8 (systematic) km s-1 Mpc-1. The systematic model uncertainty is governed by the surface-mass density (convergence) at the location of the multiple images.
The Astrophysical Journal 12/2008; 572(1):L11. · 6.02 Impact Factor
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Naohisa Inada,
Masamune Oguri,
Robert H. Becker,
Richard L. White,
Michael D. Gregg, Paul L. Schechter,
Yozo Kawano,
Christopher S. Kochanek,
Gordon T. Richards,
Donald P. Schneider, [......],
J. Brinkmann,
Michael Harvanek,
S. J. Kleinman,
Jurek Krzesinski,
Dan Long,
Eric H. Neilsen,
Jr,
Atsuko Nitta,
Stephanie A. Snedden,
and Donald G. York
[show abstract]
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ABSTRACT: We report the discoveries of two two-image gravitationally lensed quasars selected from the Sloan Digital Sky Survey: SDSS J0806+2006 at zs = 1.540 and SDSS J1353+1138 at zs = 1.629 with image separations of Δθ = 140 and Δθ = 141, respectively. Spectroscopic and optical/near-infrared imaging follow-up observations show that the quasar images have identical redshifts and possess extended objects between the images that are likely to be lens galaxies at zl 0.6 in SDSS J0806+2006 and zl 0.3 in SDSS J1353+1138. The field of SDSS J0806+2006 contains several nearby galaxies that may significantly perturb the system, and SDSS J1353+1138 has an extra component near its Einstein ring that is probably a foreground star. Simple mass models with reasonable parameters reproduce the quasar positions and fluxes of both systems.
The Astronomical Journal 12/2007; 131(4):1934. · 4.03 Impact Factor
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ABSTRACT: We report the discovery of the new double quasar CTQ 839. This B = 18.3, radio-quiet quasar pair is separated by 21 in BRI and H filters, with magnitude differences of ΔmB = 2.5, ΔmR = ΔmI = 1.9, and ΔmH = 2.3. Spectral observations reveal both components to be z = 2.24 quasars, with relative redshifts that agree at the 100 km s-1 level but exhibit pronounced differences in the equivalent widths of related emission features, as well as an enhancement of blue continuum flux in the brighter component as compared with the fainter component longward of the Lyα emission feature. In general, similar redshift double quasars can be the result of a physical binary pair or of a single quasar multiply imaged by gravitational lensing. Empirical point-spread function subtraction of R and H band images of CTQ 839 reveal no indication of a lensing galaxy and place a detection limit of R = 22.5 and H = 17.4 for a third component in the system. For an Einstein-de Sitter cosmology and singular isothermal sphere model, the R band detection limit constrains the characteristics of any lensing galaxy to zl 1 with a corresponding luminosity of L 5 L*, while an analysis based on the redshift probability distribution for the lensing galaxy argues against the existence of a zl 1 lens at the 2 σ level. A similar analysis for a Λ-dominated cosmology, however, does not significantly constrain the existence of any lensing galaxy. The broadband flux differences, spectral dissimilarities, and failure to detect a lensing galaxy make the lensing hypothesis for CTQ 839 unlikely. The similar redshifts of the two components would then argue for a physical quasar binary. At a projected separation of 8.3 h-1 kpc (Ωm = 1), CTQ 839 would be the smallest projected separation binary quasar currently known.
The Astronomical Journal 12/2007; 119(3):1083. · 4.03 Impact Factor
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ABSTRACT: We report the discovery and ground-based observations of the new gravitational lens CTQ 414. The source quasar lies at a redshift of z = 1.29 with a B magnitude of 17.6. Ground-based optical imaging reveals two point sources separated by 12 with a magnitude difference of roughly 1 mag. Subtraction of two stellar point-spread functions from images obtained in subarcsecond seeing consistently leaves behind a faint, residual object. Fits for two point sources plus an extended object places the fainter object collinear with the two brighter components. Subsequent Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) observations have confirmed the identification of the fainter object as the lensing galaxy. Very Large Array observations at 8.46 GHz reveal that all components of the lensing system are radio-quiet down to the 0.2 mJy flux level.
The Astronomical Journal 12/2007; 118(4):1444. · 4.03 Impact Factor
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Joshua N. Winn,
Jacqueline N. Hewitt, Paul L. Schechter,
Alan Dressler,
E. E. Falco,
C. D. Impey,
C. S. Kochanek,
J. Lehár,
J. E. J. Lovell,
B. A. McLeod,
Nicholas D. Morgan,
J. A. Muñoz,
H.-W. Rix,
and Maria Teresa Ruiz
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a new double-image quasar that was found during a search for gravitational lenses in the southern sky. Radio source PMN J1838-3427 is composed of two flat-spectrum components with separation 10, flux density ratio 14 : 1, and matching spectral indices in VLA and VLBA images. Ground-based BRI images show the optical counterpart (total I = 18.6) is also double, with the same separation and position angle as the radio components. An HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27 : 1) is higher than the radio value, probably because of differential extinction of the components by the lens galaxy. An optical spectrum of the bright component contains quasar emission lines at z = 2.78 and several absorption features, including prominent Lyα absorption. The lens galaxy redshift could not be measured, but it is estimated to be z = 0.36 ± 0.08. The image configuration is consistent with the simplest plausible models for the lens potential. The flat radio spectrum and observed variability of PMN J1838-3427 suggest that the time delay between flux variations of the components is measurable and could thus provide an independent measurement of H0.
The Astronomical Journal 12/2007; 120(6):2868. · 4.03 Impact Factor
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ABSTRACT: In the course of a Cycle 8 snapshot imaging survey with the Space Telescope Imaging Spectrograph (STIS), we have discovered that the z = 1.565 quasar HE 0512-3329 is a double with image separation 0644, differing in brightness by only 0.4 mag. This system is almost certainly gravitationally lensed. Although separate spectra for the two images have not yet been obtained, the possibility that either component is a Galactic star is ruled out by a high signal-to-noise composite ground-based spectrum and separate photometry for the two components: the spectrum shows no trace of any zero-redshift stellar absorption features belonging to a star with the temperature indicated by the broadband photometry. The optical spectrum shows strong absorption features of Mg II, Mg I, Fe II, Fe I, and Ca I, all at an identical intervening redshift of z = 0.9313, probably due to the lensing object. The strength of Mg II and the presence of the other low-ionization absorption features is strong evidence for a damped Lyα system, likely the disk of a spiral galaxy. Point-spread function fitting to remove the two quasar components from the STIS image leads to a tentative detection of a third object, which may be the nucleus of the lensing galaxy. The brighter component is significantly redder than the fainter, due to either differential extinction or microlensing.
The Astronomical Journal 12/2007; 119(6):2535. · 4.03 Impact Factor
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Naohisa Inada,
Robert H. Becker,
Scott Burles,
Francisco J. Castander,
Daniel Eisenstein,
Patrick B. Hall,
David E. Johnston,
Bartosz Pindor,
Gordon T. Richards, Paul L. Schechter, [......],
S. J. Kleinman,
Jurek Krzesiński,
Daniel C. Long,
Eric H. Neilsen,
Jr,
Peter R. Newman,
Atsuko Nitta,
Donald P. Schneider,
S. Snedden,
and Donald G. York
[show abstract]
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ABSTRACT: We report the discovery of a new gravitationally lensed quasar from the Sloan Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was selected from among known SDSS quasars by an algorithm that was designed to select another known SDSS lensed quasar (SDSS J1226-0006A,B). Five separate components, three of which are unresolved, are identified in photometric follow-up observations obtained with the Magellan Consortium's 6.5 m Walter Baade Telescope at Las Campanas Observatory. Two of the unresolved components (designated A and B) are confirmed to be quasars with z = 1.524; the velocity difference is less than 100 km s-1 according to spectra taken with the W. M. Keck Observatory's Keck II Telescope at Mauna Kea, Hawaii. A third stellar component, designated C, has the colors of a quasar with redshift similar to components A and B. The maximum separation of the point sources is 178. The other two sources, designated G and D, are resolved. Component G appears to be the best candidate for the lensing galaxy. Although component D is near the expected position of the fourth lensed component in a four-image lens system, its properties are not consistent with being the image of a quasar at z ~ 1.5. Nevertheless, the identical redshifts of components A and B and the presence of component C strongly suggest that this object is a gravitational lens. Our observations support the idea that a foreground object reddens the fourth lensed component and that another unmodeled effect (such as micro- or millilensing) demagnifies it, but we cannot rule out the possibility that SDSS J0924+0219 is an example of the relatively rare class of "three-component" lens systems.
The Astronomical Journal 12/2007; 126(2):666. · 4.03 Impact Factor
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ABSTRACT: We report the discovery of a gravitationally lensed quasar resulting from our survey for lenses in the southern sky. Radio images of J1632-0033 with the Very Large Array and the Australia Telescope Compact Array exhibit two compact, flat-spectrum components with separation 147 and flux density ratio 13.2. Images with the Hubble Space Telescope reveal the optical counterparts to the radio components and also the lens galaxy. An optical spectrum of the bright component obtained with the first Magellan telescope reveals quasar emission lines at redshift 3.42. Deeper radio images with the Multi-Element Radio Linked Interferometry Network and the Very Long Baseline Array reveal a faint third radio component located near the center of the lens galaxy, which is either a third image of the background quasar or faint emission from the lens galaxy.
The Astronomical Journal 12/2007; 123(1):10. · 4.03 Impact Factor
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Naohisa Inada,
Scott Burles,
Michael D. Gregg,
Robert H. Becker, Paul L. Schechter,
Daniel J. Eisenstein,
Masamune Oguri,
Francisco J. Castander,
Patrick B. Hall,
David E. Johnston,
Bartosz Pindor,
Gordon T. Richards,
Donald P. Schneider,
Richard L. White,
J. Brinkmann,
Alexander S. Szalay,
and Donald G. York
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a new two-image gravitationally lensed quasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object was selected as a lensed quasar candidate from the Sloan Digital Sky Survey (SDSS) by the same algorithm that was used to discover other SDSS lensed quasars (e.g., SDSS J0924+0219). Multicolor imaging with the Magellan Consortium's Walter Baade 6.5 m telescope and spectroscopic observations using the W. M. Keck Observatory's Keck II telescope confirm that SDSS J0246-0825 consists of two lensed images (Δθ = 104) of a source quasar at z = 1.68. Imaging observations with the Keck I telescope and the Hubble Space Telescope reveal an extended object between the two quasar components, which is likely to be a lensing galaxy of this system. From the absorption lines in the spectra of the quasar components and the apparent magnitude of the galaxy, combined with the expected absolute magnitude from the Faber-Jackson relation, we estimate the redshift of the lensing galaxy to be z = 0.724. A highly distorted ring is visible in the Hubble Space Telescope images, which is likely to be the lensed host galaxy of the source quasar. Simple mass modeling predicts the possibility that there is a small (faint) lensing object near the primary lensing galaxy.
The Astronomical Journal 12/2007; 130(5):1967. · 4.03 Impact Factor
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ABSTRACT: We report the discovery of a new double-image gravitational lens, resulting from our search for lenses in the southern sky. Radio source PMN J2004-1349 is composed of two compact components separated by 113 in VLA, MERLIN, and VLBA images. The components have a flux ratio of 1:1 at radio frequencies ranging from 5 to 22.5 GHz. The I-band optical counterpart is also an equal double, with roughly the same separation and position angle as the radio double. Upon subtraction of the components from the I-band image, we identify a dim pattern of residuals as the lens galaxy. While the present observations are sufficient to establish that PMN J2004-1349 is a gravitational lens, additional information will be necessary (such as the redshifts of the galaxy and quasar and precise astrometry and photometry of the lens galaxy) before constructing detailed mass models.
The Astronomical Journal 12/2007; 121(3):1223. · 4.03 Impact Factor
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ABSTRACT: We present our ground-based optical imaging, spectral analysis, and high-resolution radio mapping of the gravitational lens candidate FBQ 1633+3134. This z = 1.52, B = 17.7 quasar appears double on CCD images with an image separation of 066 and a relatively constant flux ratio of ~3 : 1 across B, V, R, and I filters. A single 0.27 mJy radio source is detected at 8.46 GHz, coincident within an arcsecond of both optical components, but no companion at radio wavelengths is detected for the system down to a flux level of 0.1 mJy (3 σ). Spectral observations reveal a rich metal-line absorption system consisting of a strong Mg II doublet and associated Fe I and Fe II absorption features, all at an intervening redshift of z = 0.684, suggestive of a lensing galaxy. Point-spread function subtraction of ground-based images however shows no obvious signs of a third object between the two quasar images and places a detection limit of I 23.0 if such an object exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot be ruled out, the evidence presented here is consistent with FBQ 1633+3134 being a single quasar lensed by a faint, metal-rich galaxy.
The Astronomical Journal 12/2007; 121(2):611. · 4.03 Impact Factor
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ABSTRACT: The Hamburg/ESO quasar HE 1113-0641 is found to be a quadruple gravitational lens, based on observations with the twin 6.5m Magellan telescopes at the Las Campanas Observatory, and subsequently with the Hubble Space Telescope. The z_S=1.235 quasar appears in a cross configuration, with i' band magnitudes ranging from 18.0 to 18.8. With a maximum image separation of 0.67'', this is the smallest-separation quadruple ever identified using a ground-based optical telescope. PSF subtraction reveals a faint lensing galaxy. A simple lens model succeeds in predicting the observed positions of the components, but fails to match their observed flux ratios by up to a magnitude. We estimate the redshift of the lensing galaxy to be z_L~0.7. Time delay estimates are on the order of a day, suggesting that the flux ratio anomalies are not due to variability of the quasar, but may result from substructure or microlensing in the lens galaxy.
11/2007;
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Annals of the New York Academy of Sciences 12/2006; 422(1):91 - 94. · 3.15 Impact Factor
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[show abstract]
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ABSTRACT: X-ray and optical observations of quadruply lensed quasars can provide a
microarcsecond probe of the lensed quasar, corresponding to scale sizes of
\~10^2-10^4 gravitational radii of the central black hole. This high angular
resolution is achieved by taking advantage of microlensing by stars in the
lensing galaxy. In this paper we utilize X-ray observations of ten lensed
quasars recorded with the Chandra X-ray Observatory as well as corresponding
optical data obtained with either the Hubble Space Telescope or ground-based
optical telescopes. These are analyzed in a systematic and uniform way with
emphasis on the flux-ratio anomalies that are found relative to the predictions
of smooth lens models. A comparison of the flux ratio anomalies between the
X-ray and optical bands allows us to conclude that the optical emission regions
of the lensed quasars are typically larger than expected from basic thin disk
models by factors of ~3-30.
07/2006;
