* Astronomy

Title: A search for the third lensed image in JVAS B1030+074
Authors: M. Zhang, N. Jackson, R. W. Porcas, I. W. A. Browne

Central gravitational image detection is very important for the study of the mass distribution of the inner parts (~100 pc) of lens galaxies. However, the detection of such images is extremely rare and difficult. We present a 1.7-GHz High Sensitivity Array (HSA) observation of the double-image radio lens system B1030+074. The data are combined with archive VLBA and global-VLBI observations, and careful consideration is given to the effects of noise, cleaning and self-calibration. An upper limit is derived for the strength of the central image of 180 µJy (90% confidence level), considerably greater than would have been expected on the basis of a simple analysis. This gives a lower limit of ~10³ for the ratio of the brightest image to the central image. For cusped models of lens mass distributions, we have made use of this non-detection to constrain the relation between inner power-law slope \beta of the lensing galaxy mass profile, and its break radius r_b. For r_b>130 pc the power-law slope is required to be close to isothermal (ß >1.8). A flatter inner slope is allowed if a massive black hole is present at the centre of the lensing galaxy, but the effect of the black hole is small unless it is ~10 times more massive than that implied by the relation between black hole mass and stellar velocity dispersion. By comparing four epochs of VLBI observations, we also detected possible superluminal motion in the jet in the brighter A image. The B jet remains unresolved, as expected from a simple lens model of the system.

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This example of a galaxy group lens in the CFHTLS-SL2S, called SL2SJ021408-053532, shows a very complex arc structure (in blue). Such complex arc geometries allow us to probe the details of the dark matter profiles associated with the group of yellow galaxies in the centre of the image.

© Canada-France-Hawaii Telescope Corporation

Title: Deconvolution of HST images of the Cloverleaf gravitational lens : detection of the lensing galaxy and a partial Einstein ring
Authors: Virginie Chantry, Pierre Magain

Archival HST/NICMOS-2 images of the Cloverleaf gravitational lens (H1413+117), a quadruply imaged quasar, have been analysed with a new method derived from the MCS deconvolution algorithm (Magain et al., 1998). This method is based on an iterative process which simultaneously allows to determine the Point Spread Function (PSF) and to perform a deconvolution of images containing several point sources plus extended structures. As such, it is well adapted to the processing of gravitational lens images, especially in the case of multiply imaged quasars. Two sets of data have been analysed : the first one, which has been obtained through the F160W filter in 1997, basically corresponds to a continuum image, while the second one, obtained through the narrower F180M filter in 2003, is centred around the forbidden (OIII) emission lines at the source redshift, thus probing the narrow-line region of the quasar. The deconvolution gives astrometric and photometric measurements in both filters and reveals the primary lensing galaxy as well as a partial Einstein ring. The high accuracy of the results is particularly important in order to model the lensing system and to reconstruct the source undergoing the strong lensing. The reliability of the method is checked on a synthetic image similar to H1413+117.

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Title: A Time Delay for the Largest Gravitationally Lensed Quasar: SDSS J1004+4112
Authors: J. Fohlmeister (1), C. S. Kochanek (2), E. E. Falco (3), J. Wambsganss (1), N. Morgan (2), C. W. Morgan (2 and 4), E. O. Ofek (5), D. Maoz (6), C. R. Keeton (7), J. C. Barentine (8), G. Dalton (9), J. Dembicky (8), W. Ketzeback (8), R. McMillan (8), C.S. Peters (10) ((1) Zentrum fur Astronomie der Universitat Heidelberg, (2) Department of Astronomy, Ohio State University, (3) Smithsonian Astrophysical Observatory, (4) Department of Physics, United States Naval Academy, (5) California Institute of Technology, (6) School of Physics and Astronomy and the Wise Observatory, (7) Department of Physics & Astronomy, Rutgers University, (8) Apache Point Observatory, (9) Department of Physics, University of Oxford, (10) Department of Physics and Astronomy, Dartmouth College)

Researchers present 426 epochs of optical monitoring data spanning 1000 days from December 2003 to June 2006 for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is 38.4 ±2.0 days in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured delay invalidates all published models. The models failed because they neglected the perturbations from cluster member galaxies. Models including the galaxies can fit the data well, but strong conclusions about the cluster mass distribution should await the measurement of the longer, and less substructure sensitive, delays of the C and D images. For these images, a CB delay of 681±15 days is plausible but requires confirmation, while CB and AD delays of >560 days and > 800 days are required. The researchers clearly detect microlensing of the A/B images, with the delay-corrected flux ratios changing from B-A=0.44 ±0.01 mag in the first season to 0.29 ±0.01 mag in the second season and 0.32 ±0.01 mag in the third season.

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The r-band image obtained with Minicam on January 16, 2005. The 3.3 arcmin x 3.5 arcmin field shows the lensed images of SDSS J1004+4112 and the five reference stars S1, S2, S3, S4 and S5 used for the PSF.