Revealing the structure of the lensed quasar Q 0957+561

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