Time delay and lens redshift for the doubly imaged BAL quasar SBS1520+530 (original) (raw)
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An optical time-delay for the lensed BAL quasar HE 2149-2745
Astronomy & Astrophysics, 2002
We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149−2745. The data, obtained with the 1.5m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103 ± 12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149−2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495 ± 0.01. Adopting this redshift, a Ω = 0.3, Λ = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H0 = 66 ± 8 km s −1 Mpc −1 (1σ error) with an estimated systematic error of ±3 km s −1 Mpc −1 . Using non-parametric models yields H0 = 65 ± 8 km s −1 Mpc −1 (1σ error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines -equal to 3.7 -remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy.
The lensing system towards the doubly imaged quasar SBS 1520+530
Astronomy & Astrophysics, 2002
The gravitational potential responsible for the lensing effect in SBS 1520+530 is studied over length scales from a few arc-seconds to a few arc-minutes. For this purpose, we use sharply deconvolved Hubble Space Telescope images in the optical and near-IR, in combination with ground based optical data obtained over a wider field-of-view. In particular, we have carried out a multi-color analysis in order to identify groups or clusters of galaxies along the line of sight. Photometric redshifts are measured for 139 galaxies unveiling significant excesses of galaxies 1.0 arcmin, NW and 1.7 arcmin, SW of the main lensing galaxy. The photometric redshift inferred both for the main lensing galaxy and for the galaxy concentrations is z=0.9^{+0.10}_{-0.25}. This is in rough agreement with the measured spectroscopic redshift of the main lensing galaxy, z=0.71 (Burud et al. 2002), suggesting that it is part of a larger group or cluster. We investigate the impact of including the galaxy cluster, first on the modelling of the lensing system, and second on the expected time--delay between the two quasar images.
Astronomy Letters, 2006
We present the R c-band light curves for components A and B of the gravitationally lensed quasar SBS 1520+530 obtained during 2001-2005 with the 1.5-m Russian-Turkish Telescope (RTT-150) at the TUBITAK National Observatory (Turkey). Based on an analysis of the data for the period 2001-2002, we have estimated the time delay of the brightness fluctuations between components A and B of the quasar to be 128 days. This time delay agrees with its previously published values for the periods 1999-2001 and 2003-2004. Using all of the published data on the brightnesses of components A and B of SBS 1520+530 for the 6-year period, we have found at least two microlensing events. One event has the pattern of a long-term linear trend; the duration of the other event is several hundred days.
A Two-Year Time Delay for the Lensed Quasar SDSS J1029+2623
The Astrophysical Journal, 2013
We present 279 epochs of optical monitoring data spanning 5.4 years from 2007 January to 2012 June for the largest image separation (22. ′′ 6) gravitationally lensed quasar, SDSS J1029+2623. We find that image A leads the images B and C by ∆t AB = (744 ± 10) days (90% confidence); the uncertainty includes both statistical uncertainties and systematic differences due to the choice of models. With only a ∼ 1% fractional error, the interpretation of the delay is limited primarily by cosmic variance due to fluctuations in the mean line-of-sight density. We cannot separate the fainter image C from image B, but since image C trails image B by only 2-3 days in all models, the estimate of the time delay between image A and B is little affected by combining the fluxes of images B and C. There is weak evidence for a low level of microlensing, perhaps created by the small galaxy responsible for the flux ratio anomaly in this system. Interpreting the delay depends on better constraining the shape of the gravitational potential using the lensed host galaxy, other lensed arcs and the structure of the X-ray emission.
Redshifts and lens profile for the double quasar QJ 0158-4325 ⋆ (Research Note)
2012
Aims. We report on the redshift of the lensing galaxy and of the quasar QJ 0158-4325 and on the lens model of the system. Methods. A deep VLT/FORS2 spectrum and HST/NICMOS-F160W images are deconvolved. From the images we derive the light profile of the lensing galaxy and an accurate relative astrometry for the system. In addition we measure the flux ratio between the quasar images in the Mg II emission line to constrain the mass model. Results. From the spectrum we measure the redshift of the lensing galaxy (z = 0.317 ± 0.001) and of the quasar (z = 1.294 ± 0.008). Using the flux ratio in the lens model allows to discard the SIE as a suitable approximation of the lens potential. On the contrary the truncated-PIEMD gives a good fit to the lens and leads to a time delay of ∆tA−B=-14.5±0.1 days, with H0=73 km s −1 Mpc −1. Conclusions. Using the flux ratio to constrain the mass model favors the truncated-PIEMD over the SIE, while ignoring this constraint leaves the choice open. Key word...
Redshifts and lens profile for the double quasar QJ 0158-4325
Astronomy and Astrophysics, 2009
Aims. We report on the redshift of the lensing galaxy and of the quasar QJ 0158-4325 and on the lens model of the system. Methods. A deep VLT/FORS2 spectrum and HST/NICMOS-F160W images are deconvolved. From the images we derive the light profile of the lensing galaxy and an accurate relative astrometry for the system. In addition we measure the flux ratio between the quasar images in the Mg II emission line to constrain the mass model. Results. From the spectrum we measure the redshift of the lensing galaxy (z = 0.317 ± 0.001) and of the quasar (z = 1.294 ± 0.008). Using the flux ratio in the lens model allows to discard the SIE as a suitable approximation of the lens potential. On the contrary the truncated-PIEMD gives a good fit to the lens and leads to a time delay of ∆t A−B =-14.5±0.1 days, with H 0 =73 km s −1 Mpc −1 . Conclusions. Using the flux ratio to constrain the mass model favors the truncated-PIEMD over the SIE, while ignoring this constraint leaves the choice open.
arXiv (Cornell University), 2012
We present the results from nine years of optically monitoring the gravitationally lensed z QSO = 0.658 quasar RX J1131−1231. The R-band light curves of the four individual images of the quasar were obtained using deconvolution photometry for a total of 707 epochs. Several sharp quasar variability features strongly constrain the time delays between the quasar images. Using three different numerical techniques, we measured these delays for all possible pairs of quasar images while always processing the four light curves simultaneously. For all three methods, the delays between the three close images A, B, and C are compatible with being 0, while we measured the delay of image D to be 91 days, with a fractional uncertainty of 1.5% (1σ), including systematic errors. Our analysis of random and systematic errors accounts in a realistic way for the observed quasar variability, fluctuating microlensing magnification over a broad range of temporal scales, noise properties, and seasonal gaps. Finally, we find that our time-delay measurement methods yield compatible results when applied to subsets of the data.
Astronomy and Astrophysics, 2006
Aims. To provide the observational constraints required to use the gravitationally lensed quasar SDSS J0924+0219 for the determination of H 0 from the time delay method. We measure here the redshift of the lensing galaxy, we show the spectral variability of the source, and we resolve the lensed host galaxy of the source. Methods. We present our VLT/FORS1 deep spectroscopic observations of the lensed quasar SDSS J0924+0219, as well as archival HST/NICMOS and ACS images of the same object. The two-epoch spectra, obtained in the Multi Object Spectroscopy (MOS) mode, allow for very accurate flux calibration and spatial deconvolution. This strategy provides spectra for the lensing galaxy and for the quasar images A and B, free of any mutual light contamination. We deconvolve the HST images as well, which reveal a double Einstein ring. The mass distributions in the lens, reconstructed in several ways, are compared. Results. We determine the redshift of the lensing galaxy in SDSS J0924+0219: z lens = 0.394 ± 0.001. Only slight spectral variability is seen in the continuum of quasar images A and B, while the C III], Mg II and Fe II emission lines display obvious changes. The flux ratio between the quasar images A and B is the same in the emission lines and in the continuum. One of the Einstein rings found using deconvolution corresponds to the lensed quasar host galaxy at z = 1.524 and a second bluer one, is the image either of a star-forming region in the host galaxy, or of another unrelated lower redshift object. A broad range of lens models give a satisfactory fit to the data. However, they predict very different time delays, making SDSS J0924+0219 an object of particular interest for photometric monitoring. In addition, the lens models reconstructed using exclusively the constraints from the Einstein rings, or using exclusively the astrometry of the quasar images, are not compatible. This suggests that multipole-like structures play an important role in SDSS J0924+0219.
Time delays for eleven gravitationally lensed quasars revisited
Astronomy & Astrophysics, 2011
Aims. We test the robustness of published time delays for 11 lensed quasars by using two techniques to measure time shifts in their light curves. Methods. We chose to use two fundamentally different techniques to determine time delays in gravitationally lensed quasars: a method based on fitting a numerical model and another one derived from the minimum dispersion method introduced by Pelt and collaborators. To analyse our sample in a homogeneous way and avoid bias caused by the choice of the method used, we apply both methods to 11 different lensed systems for which delays have been published: existence of a second solution on top of the published delay is revealed. The time delays in four systems, SBS 0909+523, FBQS J0951+2635, JVAS B1422+231, and HE 2149-2745 prove to be less reliable than previously claimed.
Time delay between images of the lensed quasar UM673
Astronomy & Astrophysics, 2012
Aims. We study brightness variations in the double lensed quasar UM673 (Q0142-100) with the aim of measuring the time delay between its two images. Methods. In the paper we combine our previously published observational data of UM673 obtained during the 2003-2005 seasons at the Maidanak Observatory with archival and recently observed Maidanak and CTIO UM673 data. We analyze the V, R and I-band light curves of the A and B images of UM673, which cover ten observational seasons from August 2001 to November 2010. We also analyze the time evolution of the difference in magnitudes between images A and B of UM673 over more than ten years. Results. We find that the quasar exhibits both short-term (with amplitude of ∼0.1 mag in the R band) and high-amplitude (∼0.3 mag) long-term variability on timescales of about several months and several years, respectively. These brightness variations are used to constrain the time delay between the images of UM673. From cross-correlation analysis of the A and B quasar light curves and error analysis we measure the mean time delay and its error of 89 ± 11 days. Given the input time delay of 88 days, the most probable value of the delay that can be recovered from light curves with the same statistical properties as the observed R-band light curves of UM673 is 95 +5 −16 +14 −29 days (68 and 95 % confidence intervals). Analysis of the V − I color variations and V, R and I-band magnitude differences of the quasar images does not show clear evidence of the microlensing variations between 1998 and 2010.