Jeffrey A. Blackburne

X-Ray and Optical Flux Ratio Anomalies in Quadruply Lensed Quasars. I. Zooming in on Quasar Emission Regions

X-ray and optical observations of quadruply lensed quasars can provide a microarcsecond probe of the lensed quasar, corresponding to scale sizes of ~102-104 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 use X-ray observations of 10 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.

Sizes and Temperature Profiles of Quasar Accretion Disks from Chromatic Microlensing

Microlensing perturbations to the flux ratios of gravitationally lensed quasar images can vary with wavelength because of the chromatic dependence of the accretion disks 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 8 bands ranging from 0.36 to 2.2 μm, 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.

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 ? 0.18 (at ?rest = 2018??), is significantly larger than the observed soft, (1.1-3.5 keV in the rest frame), and hard, (3.5-21.5 keV in the rest frame), band X-ray emission. There is weak evidence that the hard component is more compact than the soft, with . 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.

Further Evidence That Quasar X-Ray Emitting Regions Are Compact: X-Ray And Optical Microlensing In The Lensed Quasar Q J0158-4325

We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded a time delay measurement by conventional methods. We attempt to circumvent this limitation by the application of a Monte Carlo microlensing analysis technique, but we are only able to prove that the delay must have the expected sign (image A leads image B). Despite our failure to robustly measure the time delay, we successfully model the microlensing at optical and X-ray wavelengths to find a half-light radius for soft X-ray emission log(r(1/2), (X), (soft)/cm) = 14.3(-0.5)(+0.4), an upper limit on the half-light radius for hard X-ray emission log(r(1/2), (X), (hard)/cm) <= 14.6, and a refined estimate of the inclination-corrected scale radius of the optical R-band (rest frame 3100 angstrom) continuum emission region of log(r(s)/cm) = 15.6 +/- 0.3.

THE DARK-MATTER FRACTION IN THE ELLIPTICAL GALAXY LENSING THE QUASAR PG 1115+080

We determine the most likely dark-matter fraction in the elliptical galaxy quadruply lensing the quasar PG 1115+080 based on analyses of the X-ray fluxes of the individual images in 2000 and 2008. Between the two epochs, the A 2 image of PG 1115+080 brightened relative to the other images by a factor of 6 in X-rays. We argue that the A 2 image had been highly demagnified in 2000 by stellar microlensing in the intervening galaxy and has recently crossed a caustic, thereby creating a new pair of microimages and brightening in the process. Over the same period, the A 2 image has brightened by a factor of only 1.2 in the optical. The most likely ratio of smooth material (dark matter) to clumpy material (stars) in the lensing galaxy to explain the observations is ~90% of the matter in a smooth dark-matter component and ~10% in stars.

A Strong X-Ray Flux Ratio Anomaly in the Quadruply Lensed Quasar PG 1115+080*

PG 1115+080 is a quadruply lensed quasar at z = 1.72 whose image positions are well fit by simple models of the lens galaxy (at z = 0.31). At optical wavelengths, the bright close pair of images exhibits a modest flux ratio anomaly (factors of ~1.2-1.4 over the past 22 yr) with respect to these same models. We show here that as observed in X-rays with Chandra, the flux ratio anomaly is far more extreme, roughly a factor of 6. The contrasting flux ratio anomalies in the optical and X-ray band confirm the microlensing hypothesis and set a lower limit on the size of the optical continuum emission region that is ~10-100 times larger than expected from a thin accretion disk model.

X-Ray and Optical Flux Anomalies in the Quadruply Lensed QSO 1RXS J1131?1231

Optical and X-ray observations of the quadruply imaged quasar 1RXS J1131-1231 show flux ratio anomalies among the images of factors of ~2 in the optical and ~3-9 in X-rays. Temporal variability of the quasar seems an unlikely explanation for the discrepancies between the X-ray and optical flux ratio anomalies. The negative parity of the most affected image and the decreasing trend of the anomalies with wavelength suggest microlensing as a possible explanation; this would imply that the source of optical radiation in RXS J1131 is ~104Rg in size for a black hole mass of ~108 M?. We also present evidence for different X-ray spectral hardness ratios among the four images.

The optical, ultraviolet, and X-ray structure of the quasar HE 0435–1223

Microlensing has proved an effective probe of the structure of the innermost regions of quasars and an important test of accretion disk models. We present light curves of the lensed quasar HE 0435–1223 in the R band and in the ultraviolet (UV), and consider them together with X-ray light curves in two energy bands that are presented in a companion paper. Using a Bayesian Monte Carlo method, we constrain the size of the accretion disk in the rest-frame near- and far-UV, and constrain for the first time the size of the X-ray emission regions in two X-ray energy bands. The R-band scale size of the accretion disk is about 1015.23 cm (~23rg ), slightly smaller than previous estimates, but larger than would be predicted from the quasar flux. In the UV, the source size is weakly constrained, with a strong prior dependence. The UV to R-band size ratio is consistent with the thin disk model prediction, with large error bars. In soft and hard X-rays, the source size is smaller than ~1014.8 cm (~10rg ) at 95% confidence. We do not find evidence of structure in the X-ray emission region, as the most likely value for the ratio of the hard X-ray size to the soft X-ray size is unity. Finally, we find that the most likely value for the mean mass of stars in the lens galaxy is ~0.3 M ☉, consistent with other studies.

X-Ray And Optical Flux Ratio Anomalies In Quadruply Lensed Quasars. II. Mapping The Dark Matter Content In Elliptical Galaxies

We present a microlensing analysis of 61 Chandra observations of 14 quadruply lensed quasars. Xray ux measurements of the individual quasar images give a clean determination of the microlensing eects in the lensing galaxy and thus oer 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 a mean impact parameter Rc of 6.6 kpc from the center of the lensing galaxy. We divide the systems into smaller ensembles based on Rc and nd that the most likely local stellar fraction varies qualitatively and quantitatively as expected, decreasing as a function of Rc.

A CALIBRATION OF THE STELLAR MASS FUNDAMENTAL PLANE AT z ∼ 0.5 USING THE MICRO-LENSING-INDUCED FLUX RATIO ANOMALIES OF MACRO-LENSED QUASARS

We measure the stellar mass surface densities of early-type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs, and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single-epoch X-ray snapshots of 10 quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter initial mass function with a low-mass cutoff of 0.1 M {sub ☉} and treat the zeropoint of the surface mass density as a free parameter. Our method measures the graininess of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.23, with a one sigma confidence range, dominated by small number statistics, of 0.77