Zooming into the broad line region of the gravitationally lensed quasar QSO 2237 + 0305 ≡ the Einstein Cross
III. Determination of the size and structure of the C iv and C iii] emitting regions using microlensing⋆
D. Sluse1, R. Schmidt1, F. Courbin2, D. Hutsemékers3, G. Meylan2, A. Eigenbrod2, T. Anguita4,5, E. Agol6 and J. Wambsganss1
Astronomisches Rechen-Institut am Zentrum für Astronomie der Universität Heidelberg Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
2 Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
3 F.R.S.-FNRS, Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, B5c, 4000 Liège, Belgium
4 Centro de Astro-Ingeniería, Departamento de Astronomía y Astrofísica, P. Universidad Católica de Chile, Casilla 306, Santiago, Chile
5 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6 Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195, USA
Received: 9 November 2010
Accepted: 13 December 2010
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 light-days = 0.06 pc = 1.7 cm (at 68.3% CI). Similar values are obtained for C iii]. Relative sizes of the carbon-line and V-band continuum emitting-regions are also derived with median values of Rline/Rcont in the range 4 to 29, depending on the FWHM of the line component. 2. 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 MBH ~ 108.3 ± 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 lines / quasars: individual: QSO 2237 + 0305 / line: formation
© ESO, 2011