Zooming into the broad line region of the gravitationally lensed quasar QSO 2237 + 0305  ≡  the Einstein Cross

Abstract

Aims. We aim to use microlensing taking place in the lensed quasar QSO 2237+0305 to study the structure of the broad line region (BLR) and measure the size of the region emitting the C iv and C iii] lines. Methods. Based on 39 spectrophotometric monitoring data points obtained between Oct. 2004 and Dec. 2007, we derived lightcurves for the C iv and C iii] emission lines. We used three different techniques to analyse the microlensing signal. Different components of the lines (narrow, broad, and very broad) were identified and studied. We built a library of the simulated microlensing lightcurves that reproduce the signal observed in the continuum and in the lines provided only the source size is changed. A Bayesian analysis scheme is then developed to derive the size of the various components of the BLR. Results. 1. The half-light radius of the region emitting the C iv line is found to be R C iv ∼ 66 The size of the C iv emitting region agrees with the radius-luminosity relationship derived from reverberation mapping. Using the virial theorem, we derive the mass of the black hole in QSO 2237+0305 to be M BH ∼ 10 8.3±0.3 M . 3. We find that the C iv and C iii] lines are produced in at least 2 spatially distinct regions, the most compact one giving rise to the broadest component of the line. The broad and narrow line profiles are slightly different for C iv and C iii]. 4. Our analysis suggests a different structure for the C iv and Fe ii+iii emitting regions, with the latter produced in the inner part of the BLR or in a less extended emitting region than C iv.Key words. gravitational lensing: micro -gravitational lensing: strong -quasars: general -quasars: emission linesquasars: individual: QSO 2237+0305 -line: formation IntroductionWe know that quasars and active galactic nucleii (AGN) are powered by matter accreted onto a supermassive black hole. The accretion of material in the direct vicinity of the central black hole releases most of the quasar energy in the form of powerlaw continuum emission. Ionised gas surrounds the central accretion disc and gives rise to broad emission lines, which are used as footprints that allow the identification and classification of quasars. Our knowledge of the kinematics and physical conditions prevailing in the BLR gas remain elusive, especially because the nuclear region of quasars is still spatially unresolved with existing instrumentation.Current insights into the BLR come from various kind of studies: empirical modelling of the line shape with kinematical models, use of photo-ionisation codes to reproduce the observed flux ratios between spectral lines, spectropolarimetric observations, statistical study of the width and asymmetry of the lines, use of the principal component analysis technique, and velocity resolved reverberation mapping (e.g. Boroson & Green 1992;Sulentic et al. 2000;Smith et al. 2005;Marziani et al. 2006;Zamfir et al. 2008;Gaskell 2009Gaskell , 2010bBentz et al. 2010). Despite the development and many successes of these methods, as briefly summarise...

Structure of the Accretion Disk in the Lensed Quasar Q2237+0305 From Multi-Epoch and Multi-Wavelength Narrowband Photometry

“…However, studies of high-magnification events are likely biased toward small quasar size estimates because it is easier to obtain high magnifications with small sources (e.g., Kochanek 2004;Eigenbrod et al 2008;Blackburne et al 2011). It is also interesting to note that without considering any velocity prior (i.e., adopting a uniform prior), the size determinations of Eigenbrod et al (2008) and Anguita et al (2008) increase by a factor ∼4 (see Sluse et al 2011) but would then require cosmologically unrealistic peculiar velocities for the lens/source.…”

“…Gravitational microlensing (Chang & Refsdal 1979, 1984; see also Kochanek 2004 andWambsganss 2006) is the main tool used to estimate both parameters, either from time variability or through the wavelength dependence of the microlensing magnification. Microlensing studies (see e.g., Pooley et al 2007;Morgan et al 2010;Blackburne et al 2011Blackburne et al , 2014Blackburne et al , 2015Sluse et al 2011;Jiménez-Vicente et al 2012Hainline et al 2013;Mosquera et al 2013;MacLeod et al 2015) have found that the mean sizes of quasar accretion disks are roughly a factor of 2-3 greater than the predictions of the standard thin disk model. These differences are too large to be explained by contamination from the broad emission lines and the pseudo-continuum contributions, or scattering on scales larger than the accretion disk (Dai et al 2010;Morgan et al 2010).…”

Partial covering of the emission regions of Q 0528−250 by intervening H2 clouds

“…Reverberation mapping establishes the relationship between the size and the luminosity of the BLR and yields a typical BLR size of RBLR ∼ 0.2 pc (Kaspi et al 2007; Chelouche & Daniel 2012) for high redshift luminous quasars. Differential microlensing allows for a constraint on the accretion disk size < ∼ 3 × 10 −3 pc (Blackburne et al 2011;Jiménez-Vicente et al 2012) and for an estimation of the size of the BLR ∼ 0.1 pc (Sluse et al 2011). The observations of gamma-ray emission constrain the size of a jet constituent to a few parsecs (Abdo et al 2010).…”

Deep optical imaging and spectroscopy of the lens system SDSS J1339+1310

“…6 we show the C iii] profiles for A and B. For the A image, the signal strength is enough to fairly appreciate the expected C iii] asymmetry, with a blue-wing excess due to Al iii (λ1857) and Si iii] (λ1892) emissions (e.g., Sluse et al 2011). The line flux of A is significantly higher than the line flux of B, but the flux ratio B/A is higher than 1 in both continuum zones around the line profiles (see Fig.…”

“…2.2, and each of these three emissions is most likely generated in spatially different regions (e.g., Marziani et al 2010;Sluse et al 2011;Motta et al 2012). According to Motta et al (2012), the broad wings of a given emission line could be produced in a compact region, whereas its core is probably dominated by photons arising from the NLR and the outer parts of the BLR.…”