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 Civ and Ciii] lines. Methods. 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. Results. 1. The half-light radius of the region emitting the Civ line is found to be RCIV∼66 +110-46 light-days = 0.06+0.09-0.04 pc = 1.7+2.8-1.1×1017 cm (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/Rcont 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 MBH ∼ 108.3±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 F 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.
Áreas temáticas de ASJC Scopus
- Astronomía y astrofísica
- Ciencias planetarias y espacial