Determination of time delay from the gravitational lens B1422+231 (original) (raw)
Related papers
The Radio Wavelength Time Delay of Gravitational Lens 0957+561
The Astrophysical Journal, 1999
The gravitational lens 0957+561 was monitored with the Very Large Array from 1979 to 1997. The 6 cm light curve data from 1995-1997 and the 4 cm data from 1990-1997 are reported here. At 4 cm, the intrinsic source variations occur earlier and are twice as large as the corresponding variations at 6 cm. The VLBI core and jet components have different magnification factors, leading to different flux ratios for the varying and non-varying portions of the VLA light curves. Using both the PRHQ and Dispersion statistical techniques, we determined the time delay, core flux ratio, and excess non-varying B image flux density. The fits were performed for the 4 cm and 6 cm light curves, both individually and jointly, and we used Gaussian Monte Carlo data to estimate 68% statistical confidence levels. The delay estimates from each individual wavelength were inconsistent given the formal uncertainties, suggesting that there are unmodeled systematic errors in the analysis. We roughly estimate the systematic uncertainty in the joint result from the difference between the 6 cm and 4 cm results, giving 409 ± 30 days for the PRHQ statistic and 397 ± 20 days for the Dispersion statistic. These results are consistent with the current optical time delay of 417 ± 3 days, reconciling the long-standing difference between the optical and radio light curves and between different statistical analyses. The unmodeled systematic effects may also corrupt light curves for other lenses, and we caution that multiple events at multiple wavelengths may be necessary to determine an accurate delay in any lens system. Now that consensus has been reached regarding the time delay in the 0957+561 system, the most pressing issue remaining for determining H 0 is a full understanding of the mass distribution in the lens.
An Optical Time Delay Estimate for the Double Gravitational Lens System B1600+434
Astrophysical Journal, 2000
We present optical I-band light curves of the gravitationally lensed double QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT) between April 1998 and November 1999. The photometry has been performed by simultaneous deconvolution of all the data frames, involving a numerical lens galaxy model. Four methods have been applied to determine the time delay between the two QSO components, giving a mean estimate of \Delta_t = 51+/-4 days (95% confidence level). This is the fourth optical time delay ever measured. Adopting a Omega=0.3, Lambda=0 Universe and using the mass model of Maller et al. (2000), this time-delay estimate yields a Hubble parameter of H_0=52 (+14, -8) km s^-1 Mpc^-1 (95% confidence level) where the errors include time-delay as well as model uncertainties. There are time-dependent offsets between the two (appropriately shifted) light curves that indicate the presence of external variations due to microlensing.
Determining the time delays in the gravitational lens PG 1115+080
Astronomy Reports, 2015
A statistical analysis of published long-term photometric monitoring observations of the gravitationally lensed quasar PG 1115+080 in the optical is presented. This goal of this study is determining the time delay between variability of the quasar manifest in its various images. Light curves of the components of PG 1115+080 obtained in 2001-2006 at the Maidanak Observatory (Uzbekistan) are considered. A linear trend is observed in the light curves of all four components during 2006, with rapid brightness variations observed only in components A1 and C. This could be a consequence of microlensing or observational errors. Application of a modified cross-correlation method to the photometric data obtained in 2004-2005 yields the time delays τ BC = 22 +2 −3 days, τ AC = 12 +2 −1 days, and τ BA = 10 +2 −3 days, in agreement with results obtained earlier by Schechter et al. and Barkana for 1995-1996 light curves using two different statistical-analysis methods. However, the new values of τ BA and τ BC differ from those obtained by Vakulik et al. using the same Maidanak Observatory data. The ratio τ AC /τ BA ∼1.2, which is close to the values obtained by Barkana (∼1.13) and predicted by lens models (∼1.4); these differ from the values obtained by Schechter et al. (∼0.7) and Vakulik et al. (∼2.7).
An optical time delay for the double gravitational lens system FBQ 0951+2635
Astronomy & Astrophysics, 2005
We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of ∆τ = 16 ± 2 days (1σ) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Ωm, ΩΛ) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H0 = 60 +9 −7 (random, 1σ) ±2 (systematic) km s −1 Mpc −1 for a singular isothermal ellipsoid model and H0 = 63 +9 −7 (random, 1σ) ±1 (systematic) km s −1 Mpc −1 for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H0 = 64 +9 −7 (random, 1σ) ±14 (systematic) km s −1 Mpc −1 .
How accurate are the time delay estimates in gravitational lensing?
Astronomy and Astrophysics, 2006
We present a novel approach to estimate the time delay between light curves of multiple images in a gravitationally lensed system, based on Kernel methods in the context of machine learning. We perform various experiments with artificially generated irregularly-sampled data sets to study the effect of the various levels of noise and the presence of gaps of various size in the monitoring data. We compare the performance of our method with various other popular methods of estimating the time delay and conclude, from experiments with artificial data, that our method is least vulnerable to missing data and irregular sampling, within reasonable bounds of Gaussian noise. Thereafter, we use our method to determine the time delays between the two images of quasar Q0957+561 from radio monitoring data at 4 cm and 6 cm, and conclude that if only the observations at epochs common to both wavelengths are used, the time delay gives consistent estimates, which can be combined to yield 408 ± 12 days. The full 6 cm dataset, which covers a longer monitoring period, yields a value which is 10% larger, but this can be attributed to differences in sampling and missing data.
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.
The Astrophysical Journal, 1999
We present the results of a program to monitor the four-image gravitational lens B1608+656 with the VLA. The system was observed over a seven month period from 1996 October to 1997 May. The 64 epochs of observation have an average spacing of 3.6 d. The light curves of the four images of the background source show that the flux density of the background source has varied at the ∼5% level. We measure time delays in the system based on common features that are seen in all four light curves. The three independent time delays in the system are found to be ∆t BA = 31±7 d, ∆t BC = 36±7 d, and ∆t BD = 76 +9
2011
We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measured Delta_t(BC) = 7.8+/-0.8 days, Delta_t(BD) = -6.5+/-0.7 days and Delta_t_CD = -14.3+/-0.8 days. We spacially deconvolved HST NICMOS2 F160W images to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. We combined these images with a stellar population fitting of a deep VLT spectrum of the lensing galaxy to estimate the baryonic fraction, f_b, in the Einstein radius. We measured f_b = 0.65+0.13-0.10 if the lensing galaxy has a Salpeter IMF and f_b = 0.45+0.04-0.07 if it has a Kroupa IMF. The spectrum also allowed us to estimate the velocity dispers...
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.