Revealing the structure of the lensed quasar Q 0957+561: I. Accretion disk size

We aim to use signatures of microlensing induced by stars in the foreground lens galaxy to infer the size of the accretion disk in the gravitationally lensed quasar Q 0957+561. The long-term photometric monitoring of this system (which so far has provided the longest available light curves of a gravitational lens system) permits us to evaluate the impact of uncertainties on our recently developed method (controlled by the distance between the modeled and the experimental magnitude difference histograms between two lensed images), and thus to test the robustness of microlensing-based disk-size estimates. We analyzed the well-sampled 21-year GLENDAMA optical light curves of the double-lensed quasar and studied the intrinsic and extrinsic continuum variations. Using accurate measurements for the time delay between the images A and B, we modeled and removed the intrinsic quasar variability, and from the statistics of microlensing magnifications we used a Bayesian method to derive the size of the region emitting the continuum at 2558 angstroms. Analyses of the Q 0957+561 R-band light curves show a slow but systematic increase in the brightness of the B relative to the A component during the past ten years. The relatively low strength of the magnitude differences between the images indicates that the quasar has an unusually big optical accretion disk of half-light radius $R_{1/2} = 17.6 pm 6.1 sqrt{M/0.3M_odot}$ lt-days.

Revealing the structure of the lensed quasar Q 0957+561: III. SMBH mass via gravitational redshift

We intend to use the impact of microlensing on the Fe III emission line blend along with a measure of its gravitational redshift to estimate the mass of the quasars central supermassive black hole (SMBH). We fit the Fe III feature in multiple spectroscopic observations between 2008 and 2016 of the gravitationally lensed quasar Q 0957+561 with relatively high signal-to-noise ratios (at the adequate wavelength). Based on the statistics of microlensing magnifications, we used a Bayesian method to derive the size of its emitting region. The Fe III spectral feature appears systematically redshifted in all epochs of observation by a value of 17 angstroms on average. We find clear differences in the shape of the Fe III line blend between images A and B. Measuring the strength of those magnitude differences, we conclude that this blend may arise from a region of half-light radius of 15 lt-days, which is in good agreement with the accretion disk dimensions for this system. We obtain a mass for the central SMBH of (1.5 +/- 0.5) x 10^9 solar masses, consistent within uncertainties with previous mass estimates based on the virial theorem. The relatively small uncertainties in the mass determination (< 35%) make this method a compelling alternative to other existing techniques (e.g., the virial plus reverberation mapping based size) for measuring black hole masses. Combining the Fe III redshift-based method with the virial, we estimate a virial factor in the 1.2 to 1.7 range for this system.

Microlensing of the broad emission lines in 27 gravitationally lensed quasars. Broad line region structure and kinematics

We aim to study the structure and kinematics of the broad line region (BLR) of a sample of 27 gravitationally lensed quasars with up to five different epochs of observation. This sample is composed of ~100 spectra from the literature plus 22 unpublished spectra of 11 systems. We measure the magnitude differences in the broad emission line (BEL) wings and statistically model the distribution of microlensing magnifications to determine a maximum likelihood estimate for the sizes of the C IV, C III], and Mg II emitting regions. The BELs in lensed quasars are expected to be magnified differently owing to the different sizes of the regions from which they originate. Focusing on the most common BELs in our spectra (C IV, C III], and Mg II), we find that the low-ionization line Mg II is only weakly affected by microlensing. In contrast, the high-ionization line C IV shows strong microlensing in some cases, indicating that its emission region is more compact. Thus, the BEL profiles are deformed differently depending on the geometry and kinematics of the corresponding emitting region. We detect microlensing in either the blue or the red wing (or in both wings with different amplitudes) of C IV in more than 50% of the systems and find outstanding asymmetries in the wings of QSO 0957+561, SDSS J1004+4112, SDSS J1206+4332, and SDSS J1339+1310. This observation indicates that the BLR is, in general, not spherically symmetric and supports the existence of two regions in the BLR, one insensitive to microlensing and another that only shows up when it is magnified by microlensing.

Size of the accretion disk in the gravitationally lensed quasar SDSS J1004+4112 from the statistics of microlensing magnifications

We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between December 2003 and October 2010. Using measured time delays for the images A, B and C and the model predicted time delay for image D we have removed the intrinsic quasar variability, finding microlensing events of about 0.5 and 0.7 mag of amplitude in the images C and D. From the statistics of microlensing amplitudes in images A, C, and D, we have inferred the half-light radius (at {lambda} rest = 2407 {AA}) for the accretion disk using two different methods, $R_{1/2}=8.7^{+18.5}_{-5.5} sqrt{M/0.3 M_odot}$ (histograms product) and $R_{1/2} = 4.2^{+3.2}_{-2.2} sqrt{M/0.3 M_odot}$ light-days ($chi^2$). The results are in agreement within uncertainties with the size predicted from the black hole mass in SDSS J1004+4112 using the thin disk theory.