An optical time-delay for the lensed BAL quasar HE 2149-2745

Abstract

Abstract. 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 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(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.

Results of optical monitoring of 5 SDSS double QSOs with the Nordic Optical Telescope

“…The algorithm has been implemented in various analysis of quasars (Burud et al 2000(Burud et al , 2002aHjorth et al 2002;Jakobsson et al 2005;Vuissoz et al 2007;Eigenbrod et al 2006a).…”

Microlensing of the broad line region in 17 lensed quasars

“…The latter have indeed been observed (e.g. Wisotzki et al 1993;Claeskens et al 2001;Burud et al 2002;Wucknitz et al 2003). The effect on the broad line emitting region (BLR) has been first addressed by Nemiroff (1988) who calculated the changes produced by a single microlensing-star on the emission lines.…”

Galaxy Groups towards Lensed Quasars

“…It has an angular separation of 1.56". The main lensing galaxy at z=0.71 (Burud et al 2002) clearly appeared after deconvolution as well as a secondary lensing galaxy , galaxy M, at 2.5" to quasar image A (Faure et al 2002). A galaxy group was discovered at 1' NorthWest to the quasar images at z phot =0.9 +0.1 −0.25 (Faure et al 2002).…”

“…A galaxy group was discovered at 1' NorthWest to the quasar images at z phot =0.9 +0.1 −0.25 (Faure et al 2002). Using the time delay between the quasar images (∆t=130±3 days, Burud et al 2002) we fit two models for the lensing potential. The first model only consider the lensing galaxy L (modeled by a Pseudo Isothermal Elliptical Mass Distribution, PIEMD, Kassiola & Kovner 1993), while the second model consider galaxy L, galaxy M and the galaxy group C (all fitted by a PIEMD).…”