2011A&A...528A.100S

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 CIV and CIII] lines. Based on 39 spectrophotometric monitoring data points obtained between Oct. 2004 and Dec. 2007, we derived lightcurves for the CIV and CIII] 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. 1. The half-light radius of the region emitting the CIV line is found to be R_CIV∼66⁺¹¹⁰_–46light-days = 0.06^+0.09_–0.04pc = 1.7^+2.8_–1.1x10¹⁷cm (at 68.3% CI). Similar values are obtained for CIII]. Relative sizes of the carbon-line and V-band continuum emitting-regions are also derived with median values of R^line/R^cont in the range 4 to 29, depending on the FWHM of the line component. 2. The size of the CIV 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 CIV and CIII] 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 CIV and CIII]. 4. Our analysis suggests a different structure for the CIV and FeII+III emitting regions, with the latter produced in the inner part of the BLR or in a less extended emitting region than CIV.