Related papers: Time delay in QSO 0957+561 from 1984-99 optical da…
From optical R band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (about 330 days of overlap between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image).…
CCD photometry of the gravitational lens system 0957+561A,B in the g and r bands was obtained on alternate nights, weather permitting, from December 1994 through May 1995 using the Double Imaging Spectrograph (DIS) on the Apache Point…
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 16 +/- 2 days (1 sigma) is…
We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi^2 minimization between the data and a numerical model light curve. A linear variation can be included in order to correct for…
Longtime monitoring of gravitational lens systems is often done using telescopes and recording equipment with modest resolution. Still, it would be interesting to get as much information as possible from the measured lightcurves. From high…
Aims: Our aim is to measure the time delay between the two gravitationally lensed images of the z = 1.547 quasar SDSS J1650+4251, in order to estimate the Hubble constant H_0. Methods: Our measurement is based on R-band light curves with 57…
We present optical lightcurves of the gravitationally lensed components A (=A1+A2+A3) and B of the quadruple quasar RX J0911.4+0551 (z = 2.80). The observations were primarily obtained at the Nordic Optical Telescope between 1997 March and…
We present new results from extremely deep, high-resolution images of the field around the double quasar QSO 0957+561. A possible gravitational arc system near the double quasar has recently been reported, which, if real, would set strong…
From regular monitoring of the Double Quasar QSO 0957+561 A,B there is now general agreement on a time delay of about 416 days. This has made it possible to determine the microlensing residual in the light-curve, see Pelt et al. (1998). We…
The time delays between the components of a lensed quasar are basic tools to analyze the expansion of the Universe and the structure of the main lens galaxy halo. In this paper, we focus on the variability and time delay of the double…
We have measured the time delay between the two images of the gravitationally lensed quasar HE1104-1805 by combining observations made with the Wise Observatory 1m telescope and published observations of this system by Schechter et al.,…
We report first results from an ongoing monitoring campaign to measure time delays between the six images of the quasar SDSS\,J2222$+$2745, gravitationally lensed by a galaxy cluster. The time delay between A and B, the two most highly…
The lensed double QSO 0957+561 has a well-measured time delay and hence is useful for a global determination of H0. Uncertainty in the mass distribution of the lens is the largest source of uncertainty in the derived H0. We investigate the…
We report an increase of more than 0.2 mag in the optical brightness of the leading image (A) of the gravitational lens Q0957+561, detected during the 09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening is…
Measurement of the time delay between multiple images of a gravitational lens system is potentially an accurate method of determining the Hubble constant over cosmological distances. One of the most promising candidates for an application…
We present first results from five years of spectrophotometric monitoring of the bright double QSO and gravitational lens HE 1104-1805. The quasar has varied considerably over this time, while the emission line fluxes appear to have…
High precision VLA flux density measurements for the lensed images of 0218+357 yield a time delay of 10.1(+1.5-1.6)days (95% confidence). This is consistent with independent measurements carried out at the same epoch (Biggs et al. 1999),…
The quadruple quasar H1413+117 (z_s = 2.56) has been monitored with the 2.0 m Liverpool Telescope in the r Sloan band from 2008 February to July. This optical follow-up leads to accurate light curves of the four quasar images (A-D), which…
The light curves of the two images of the double quasar Q0957+561 as obtained by Kundic et al. (1997) are almost identical, except for an overall time delay and scaling factor. This allows us to put limits on the amount of microlensing that…
We re-analyze brightness data sampled intensively over 5 nights at two epochs separated by the quasar lens time delay, to examine the nature of the observed microlensing. We find strong evidence for a microlensing event with an amplitude of…