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We present results from a monitoring campaign performed with the Chandra X-ray Observatory of the gravitationally lensed quasars RX J1131-1231 and HE 1104-1805. We detect significant X-ray variability in all images of both quasars. The flux variability detected in image A of RX J1131-1231 is of particular interest because of its high amplitude (a factor of ~ 20). We interpret it as arising from microlensing since the variability is uncorrelated with that of the other images and the X-ray flux ratios show larger changes than the optical as we would expect for microlensing of the more compact X-ray emission regions. The differences between the X-ray and optical flux ratios of HE 1104-1805 are less dramatic, but there is no significant soft X-ray or dust absorption, implying the presence of X-ray microlensing in this system as well. Combining the X-ray data with the optical light curves we find that the X-ray emitting region of HE 1104-1805 is compact with a half-light radius ~ 6 r_g, where the gravitational radius is r_g = 3.6 x 10^14 cm, thus placing significant constraints on AGN corona models. We also find that the microlensing in HE 1104-1805 favors mass models for the lens galaxy that are dominated by dark matter. Finally, we better characterize the massive foreground cluster near RX J1131-1231, set limits on other sources of extended X-ray emission, and limit the fluxes of any central odd images to be 30-50 (3 sigma) times fainter than the observed images.
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We present results of the long term monitoring of the gravitationally lensed quasar HE1104-1805. The photometric data were collected between August 1997 and January 2002 as a subproject of the OGLE survey. We determine the time delay in the light curves of images A and B of HE1104-1805 to be equal to 157+/-21 days with the variability in the image B light curve leading variability of the image A. The result is in excellent agreement with the earlier determination by Ofek and Maoz. OGLE photometry of HE1104-1805 is available to the astronomical community from the OGLE Internet archive.
We present a new determination of the time delay of the gravitational lens system HE1104-1805 (Double Hamburger) based on a previously unpublished dataset. We argue that the previously published value of dt_(A-B)=0.73 years was affected by a bias of the employed method. We determine a new value of dt_(A-B)=0.85+/-0.05 years (2 sigma confidence level), using six different techniques based on non interpolation methods in the time domain. The result demonstrates that even in the case of poorly sampled lightcurves, useful information can be obtained with regard to the time delay. The error estimates were calculated through Monte Carlo simulations. With two already existing models for the lens and using its recently determined redshift, we infer a range of values of the Hubble parameter: Ho=48+/-4 km/s Mpc^-1 (2 sigma) for a singular isothermal ellipsoid (SIE) and Ho=62+/-4 km/s Mpc^-1 (2 sigma) for a constant mass-to-light ratio plus shear model (M/L+gamma). The possibly much larger errors due to systematic uncertainties in modeling the lens potential are not included in this error estimate.
Optical and X-ray observations of the quadruply imaged quasar 1RXS J1131-1231 show flux ratio anomalies among the images 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 ~10^4 R_g in size for a black hole mass of ~10^8 M_sun. We also present evidence for different X-ray spectral hardness ratios among the four images.
The gravitationally lensed quasar HE 1104-1805 has been observed at a variety of wavelengths ranging from the mid-infrared to X-ray for nearly 20 years. We combine flux ratios from the literature, including recent Chandra data, with new observations from the SMARTS telescope and HST, and use them to investigate the spatial structure of the central regions using a Bayesian Monte Carlo analysis of the microlensing variability. The wide wavelength coverage allows us to constrain not only the accretion disk half-light radius r_1/2, but the power-law slope xi of the size-wavelength relation r_1/2 ~ lambda^xi. With a logarithmic prior on the source size, the (observed-frame) R-band half-light radius log(r_1/2/cm) is 16.0+0.3-0.4, and the slope xi is 1.0+0.30-0.56. We put upper limits on the source size in soft (0.4-1.2 keV) and hard (1.2-8 keV) X-ray bands, finding 95% upper limits on log (r_1/2/cm) of 15.33 in both bands. A linear prior yields somewhat larger sizes, particularly in the X-ray bands. For comparison, the gravitational radius, using a black hole mass estimated using the Hbeta line, is log(r_g/cm) = 13.94. We find that the accretion disk is probably close to face-on, with cos i = 1.0 being four times more likely than cos i = 0.5. We also find probability distributions for the mean mass of the stars in the foreground lensing galaxy, the direction of the transverse peculiar velocity of the lens, and the position angle of the projected accretion disks major axis (if not face-on).
We present the main results of the first long-term spectrophotometric monitoring of the ``Einstein cross Q2237+0305 and of the single-epoch spectra of the lensed quasar J1131-1231. From October 2004 to December 2006, we find that two prominent microlensing events affect images A & B in Q2237+0305 while images C & D remain grossly unaffected by microlensing on a time scale of a few months. Microlensing in A & B goes with chromatic variations of the quasar continuum. We observe stronger micro-amplification in the blue than in the red part of the spectrum, as expected for continuum emission arising from a standard accretion disk. Microlensing induced variations of the CIII] emission are observed both in the integrated line intensity and profile. Finally, we also find that images C & D are about 0.1-0.3 mag redder than images A & B. The spectra of images A-B-C in J1131-1231 reveal that, in April 2003, microlensing was at work in images A and C. We find that microlensing de-amplifies the continuum emission and the Broad Line Region (BLR) in these images. Contrary to the case of Q2237+0305, we do not find evidence for chromatic microlensing of the continuum emission. On the other hand, we observe that the Balmer and MgII broad line profiles are deformed by microlensing. These deformations imply an anti-correlation between the width of the emission line and the size of the corresponding emitting region. Finally, the differential microlensing of the FeII emission suggests that the bulk of FeII is emitted in the outer parts of the BLR while another fraction of FeII is produced in a compact region.
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