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See detailPhotometric monitoring of the doubly imaged quasar UM 673: possible evidence for chromatic microlensing
Nakos, Theodoros; Courbin, F.; Poels, Joël ULg et al

in Astronomy and Astrophysics (2005), 441

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i ... [more ▼]

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998-September 1999) and in the Johnson V-band (October 1998 to December 2001), were analyzed using three different photometric methods. The light-curves obtained with all methods show variations, with a peak-to-peak amplitude of 0.14 mag in V. Although it was not possible to measure the time delay between the two lensed QSO images, the brighter component displays possible evidence for microlensing: it becomes bluer as it gets brighter, as expected under the assumption of differential magnification of a quasar accretion disk. [less ▲]

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See detailAn optical time delay for the double gravitational lens system FBQ 0951+2635
Jakobsson, P.; Hjorth, J.; Burud, I. et al

in Astronomy and Astrophysics (2005), 431(1), 103-109

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 ... [more ▼]

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 Deltatau = 16 +/- 2 days (1sigma) 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 (Omega(m), Omega(Lambda)) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H-0 = 60(-7)(+9) (random, 1sigma) +/-2 (systematic) km s(-1) Mpc(-1) for a singular isothermal ellipsoid model and H-0 = 63(-7)(+9) (random, 1sigma) +/-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 H-0 = 64(-7)(+9) (random, 1sigma) +/- 14 (systematic) km s(-1) Mpc(-1). [less ▲]

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See detailOn-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228, at z=0.135
Courbin, F.; Letawe, Géraldine ULg; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2002), 394

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ... [more ▼]

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z=0.135 (M[SUB]B[/SUB]=-23.0), it provides us with the spectrum of the host galaxy between 3600 Å and 8500 Å (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4\arcsec away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1 kpc) = (2.0 +/- 0.3)x 10[SUP]10[/SUP] M[SUB]sun[/SUB] within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10 kpc) = (1.9 +/- 0.3) x 10[SUP]11[/SUP] M[SUB]sun[/SUB], with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228, is a normal spiral galaxy. Based on observations made with ANTU/UT1 at ESO-Paranal observatory in Chile (program 65.P-0361(A)), and with the ESO 3.5 m NTT, at La Silla observatory (program 62.P-0643(B)). [less ▲]

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See detailTime delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530
Burud, I.; Hjorth, J.; Courbin, F. et al

in Astronomy and Astrophysics (2002), 391

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ... [more ▼]

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ) is determined from the light curves. In addition, spectra of <ASTROBJ>SBS 1520+530</ASTROBJ> obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z=0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega =0.3, Lambda =0.7 cosmology, our time-delay measurement yields a Hubble constant of H[SUB]0[/SUB]=51 +/- 9 km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (1sigma error). Based on observations made with the Nordic Optical, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias and the W. M. Keck Observatory which is operated jointly by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/481 [less ▲]

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See detailAn optical time-delay for the lensed BAL quasar HE 2149-2745
Burud, I.; Courbin, F.; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2002), 383(1), 71-81

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000 ... [more ▼]

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m 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 Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma 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. [less ▲]

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See detailA novel approach for extracting time-delays from lightcurves of lensed quasar images
Burud, I.; Magain, Pierre ULg; Sohy, Sandrine ULg et al

in Astronomy and Astrophysics (2001), 380

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear ... [more ▼]

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on chi [SUP]2[/SUP] minimization between the data and a numerical model light curve. A linear variation can be included in order to correct for slow long-term microlensing effects in one of the lensed images. An iterative version of the method can be applied in order to correct for higher-order microlensing effects. The method is tested on simulated light curves. When higher-order microlensing effects are present, the time delay is best constrained with the iterative method. Analysis of a published data set for the lensed double Q 0957+561 yields results in agreement with other published estimates. [less ▲]

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See detailAn Optical Time Delay Estimate for the Double Gravitational Lens System B1600+434
Burud, I.; Hjorth, J.; Jaunsen, A. O. et al

in Astrophysical Journal (2000), 544

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 1998 April and 1999 November. The ... [more ▼]

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 1998 April and 1999 November. 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 Deltat=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., this time delay estimate yields a Hubble parameter of H[SUB]0[/SUB]=52[SUP]+14[/SUP][SUB]-8[/SUB] km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (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. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. [less ▲]

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See detailLensed quasars: a matter of resolution
Courbin, F.; Lidman, C.; Burud, I. et al

in The Messenger (2000), 101

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See detailAbout the origin of extinction in the gravitational lens system MG J0414+0534
Angonin-Willaime, M.-C.; Vanderriest, C.; Courbin, F. et al

in Astronomy and Astrophysics (1999), 347

Photometric measurements of the highly reddened gravitational mirage MG J0414+0534 have been carried out either by PSF subtraction or by applying accurate deconvolution algorithms to optical (R, I) and ... [more ▼]

Photometric measurements of the highly reddened gravitational mirage MG J0414+0534 have been carried out either by PSF subtraction or by applying accurate deconvolution algorithms to optical (R, I) and near-infrared (K) images obtained at CFHT and NOT under sub-arcsecond seeing conditions. It is confirmed that the close pair of images A1-A2 suffers a larger extinction than B and C. While the colours of image A2 obtained from ground-based data seem inconsistent with a simple reddening law, higher resolution images available from HST archives reveal an additional extended component (arc) which introduces significant errors in the photometric decomposition. When the arc component is properly taken into account, the colours of the 4 nucleus images do agree with a classical reddening law, with A2 being by far the most obscured component. Such a differential extinction (maximum difference Delta E(R-I) =~ 0.6) is likely due to the lensing galaxy. This does not mean that {all} the extinction occurs into the lens. Indeed, the fact that the arc is much less red than the images of the nucleus suggests that an important part of the reddening is intrinsic to the source. Finally, no significant variability is observed within this data set, i.e. between 1994 and 1997, while a discrepancy from earlier data is noticed for (A1 + A2). Based on observations collected with the Canada-France-Hawaii Telescope at Mauna Kea (Hawaii, USA), the Nordic Optical Telescope (Canary, Spain) and archive data from the Hubble Space Telescope (NASA/ESA) [less ▲]

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See detailImage deconvolution of lensed QSOs observed with the NOT: Competing with the HST
Burud, I.; Courbin, F.; Magain, Pierre ULg

in Karttunen, H.; Piirola, V. (Eds.) Astrophysics with the NOT, Proceedings of the conference held in Turku (1999)

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See detailThree photometric methods tested on ground-based data of Q 2237+0305
Burud, I.; Stabell, R.; Magain, Pierre ULg et al

in Astronomy and Astrophysics (1998), 339

The Einstein Cross, Q 2237+0305, has been photometrically observed in four bands on two successive nights at NOT (La Palma, Spain) in October 1995. Three independent algorithms have been used to analyse ... [more ▼]

The Einstein Cross, Q 2237+0305, has been photometrically observed in four bands on two successive nights at NOT (La Palma, Spain) in October 1995. Three independent algorithms have been used to analyse the data: an automatic image decomposition technique, a CLEAN algorithm and the new MCS deconvolution code. The photometric and astrometric results obtained with the three methods are presented. No photometric variations were found in the four quasar images. Comparison of the photometry from the three techniques shows that both systematic and random errors affect each method. When the seeing is worse than 1farcs0 , the errors from the automatic image decomposition technique and the Clean algorithm tend to be large (0.04-0.1 magnitudes) while the deconvolution code still gives accurate results (1sigma error below 0.04) even for frames with seeing as bad as 1farcs7 . Reddening is observed in the quasar images and is found to be compatible with either extinction from the lensing galaxy or colour dependent microlensing. The photometric accuracy depends on the light distribution used to model the lensing galaxy. In particular, using a numerical galaxy model, as done with the MCS algorithm, makes the method less seeing dependent. Another advantage of using a numerical model is that eventual non-homogeneous structures in the galaxy can be modeled. Finally, we propose an observational strategy for a future photometric monitoring of the Einstein Cross. Based on observations obtained at NOT, La Palma. [less ▲]

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See detailHigh-Resolution Optical and Near-Infrared Imaging of the Quadruple Quasar RX J0911.4+0551
Burud, I.; Courbin, F.; Lidman, C. et al

in Astrophysical Journal (1998), 501

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular ... [more ▼]

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular separation. Raw and deconvolved data reveal an elongated lens galaxy. The observed reddening in at least two of the four QSO images suggests differential extinction by this lensing galaxy. We show that both an ellipticity of the galaxy ( epsilon _{{min}}=0.075 ) and an external shear ( gamma _{{min}}=0.15 ) from a nearby mass have to be included in the lensing potential in order to reproduce the complex geometry observed in RX J0911.4+0551. A possible galaxy cluster is detected about 38" from RX J0911.4+0551 and could contribute to the X-ray emission observed by ROSAT in this field. The color of these galaxies indicates a plausible redshift in the range of 0.6-0.8. [less ▲]

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See detailRX J0911.4+0551: a complex quadruply imaged gravitationally lensed QSO.
Burud, I.; Courbin, F.; Lidman, C. et al

in The Messenger (1998), 92

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from ... [more ▼]

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from the 2.56-m Nordic Optical Telescope, and on the NTT/SOFI data of the object. Careful deconvolution of the data allows to clearly resolve the object into four QSO components and a lensing galaxy. [less ▲]

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