Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 ≡the Einstein Cross

Abstract

We present the continuation of our long-term spectroscopic monitoring of the gravitationally lensed quasar QSO 2237+0305. We investigate the chromatic variations observed in the UV/optical continuum of both quasar images A and B, and compare them with numerical simulations to infer the energy profile of the quasar accretion disk. Our procedure combines the microlensing ray-shooting technique with Bayesian analysis, and derives probability distributions for the source sizes as a function of wavelength. We find that the effective caustic crossing timescale is 4.0 ± 1.0 months. Using a robust prior on the effective transverse velocity, we find that the source responsible for the UV/optical continuum has an energy profile well reproduced by a power-law R ∝ λ ζ with ζ = 1.2 ± 0.3, where R is the source size responsible for the emission at wavelength λ. This is the first accurate, model-independent determination of the energy profile of a quasar accretion disk on such small scales.

The different origins of high- and low-ionization broad emission lines revealed by gravitational microlensing in the Einstein cross

“…The H-band magnitudes of the telluric standard stars are listed in the 2MASS Point Source Catalog so that the flux calibration can be performed. Since we are only interested in the spectral distortions caused by gravitational microlensing, we corrected for the dust extinction in the lensing galaxy following Eigenbrod et al (2008a): while images A and B were found to be free of significant reddening, images C and D were corrected using a Cardelli law with (A V , R V ) = (0.2 mag, 3.1).…”

“…A detailed description of the observation strategy and data reduction can be found in Eigenbrod et al (2008a). For our analysis, we solely consider the spectra acquired on October 11 2005 2 .…”

“…In the following subsections, we study the effect of microlensing on the line profiles using the macro-micro decomposition (MmD) method and the narrowband technique, which have the advantage of making no assumption on the line profiles. The multi-component decomposition (MCD), used in previous microlensing studies (Eigenbrod et al 2008a;Sluse et al 2011), does not appear to be well suited because this method only involves symmetric Gaussian functions that cannot reproduce the asymmetric magnification of the Balmer line profile caused by microlensing (see Sect. 3.1.2).…”

Microlensing of the broad line region in 17 lensed quasars

“…In order to provide a more global overview of the variety of signals which may be observed, we completed our main sample with five systems we studied elsewhere: SDSS J0924+0219 (Eigenbrod et al 2006a), H1413+117 (Hutsemékers et al 2010), J1131-1231 (Sluse et al 2007), HE 2149-2745 (Burud et al 2002), and Q2237+0305 (Eigenbrod et al 2008;Sluse et al 2011). This is not a complete list of known microlensed quasars (see e.g.…”

“…After the first detection of microlensing in the continuum and in the broad line (Irwin et al 1989;Filippenko 1989), microlensing has started to be used as a tool to constrain the size of the accretion disc and of the broad line emitting region Wyithe et al 2000b;Yonehara 2001;Wyithe et al 2000a). In the last decade, important progress in observational techniques allowed photometric and spectrophotometric monitoring of the individual lensed images to be successfully carried out (Woźniak et al 2000;Dai et al 2003;Anguita et al 2008b;Eigenbrod et al 2008;Zimmer et al 2011). On the other hand, the development of more advanced numerical techniques allowed quicker calculation of magnification maps and more sophisticated analysis (Kochanek 2004;Poindexter & Kochanek 2010a,b;Bate et al 2010;Mediavilla et al 2011;Garsden et al 2011;Bate & Fluke 2012).…”