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Register a new userX-Ray and Optical Flux Anomalies in the Quadruply Lensed QSO 1RXS J1131-1231
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Jeffrey A. Blackburne n MIT
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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.
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We have observed the quadruply lensed quasar 1RXS J1131-1231 with the integral field spectrograph mode of the Kyoto Tridimensional Spectrograph II mounted on the Subaru telescope. Its field of view has covered simultaneously the three brighter lensed images A, B, and C, which are known to exhibit anomalous flux ratios in their continuum emission. We have found that the [OIII] line flux ratios among these lensed images are consistent with those predicted by smooth-lens models. The absence of both microlensing and millilensing effects on this [OIII] narrow line region sets important limits on the mass of any substructures along the line of sight, which is expressed as M_E < 10^5 M_solar for the mass inside an Einstein radius. In contrast, the H_beta line emission, which originates from the broad line region, shows an anomaly in the flux ratio between images B and C, i.e., a factor two smaller C/B ratio than predicted by smooth-lens models. The ratio of A/B in the H_beta line is well reproduced. We show that the anomalous C/B ratio for the H_beta line is caused most likely by micro/milli-lensing of image C. This is because other effects, such as the differential dust extinction and/or arrival time difference between images B and C, or the simultaneous lensing of another pair of images A and B, are all unlikely. In addition, we have found that the broad H_beta line of image A shows a slight asymmetry in its profile compared with those in the other images, which suggests the presence of a small microlensing effect on this line emitting region of image A.
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.
We present results from X-ray observations of the quadruply lensed quasar RX J0911.4+0551 using data obtained with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-ray Observatory. The 29 ks observation detects a total of ~404 X-ray photons (0.3 to 7.0 keV) from the four images of the lensed quasar. Deconvolution of the aspect corrected data resolves all four lensed images, with relative positions in good agreement with optical measurements. When compared to contemporaneous optical data, one of the lensed images (component A3) is dimmer by a factor of ~6 in X-rays with respect to the 2 brighter images (components A1 and A2). Spectral fitting for the combined images shows significant intrinsic absorption in the soft (0.2 to 2.4 keV) energy band, consistent with the mini-BAL nature of this quasar, while a comparison with ROSAT PSPC observations from 1990 shows a drop of ~6.5 in the total soft bandpass flux. The observations also detect ~157 X-ray photons arising from extended emission of the nearby cluster (peaked ~42 SW of RXJ0911.4+0551) responsible for the large external shear present in the system. The Chandra observation reveals the cluster emission to be complex and non-spherical, and yields a cluster temperature of kT = 2.3^{+1.8}_{-0.8} keV and a 2.0 to 10 keV cluster luminosity within a 1 Mpc radius of L_X = 7.6_{-0.2}^{+0.6} x 10^{43} ergs/s (error bars denote 90% confidence limits). Our mass estimate of the cluster within its virial radius is 2.3^{+1.8}_{-0.7} x 10^{14} solar, and is a factor of 2 smaller than, although consistent with, previous mass estimates based on the observed cluster velocity dispersion.
So far the lens J1131-1231 has been studied only at optical and X-ray wavelengths. A detection in the radio was almost missed as a result of an incorrect position and archive problems. A direct analysis of NVSS uv data - in contrast to the catalogue or images alone - provided sufficient evidence of a detection to justify further radio investigations. The system was subsequently observed with MERLIN and the EVN in e-VLBI mode. Even though MERLIN seems to show the lensed star-forming regions and the compact cores, a preliminary analysis of the EVN data only shows an AGN in the lens itself but not the lensed cores. Additional VLA observations will be carried out soon.
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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