EDP Sciences
Free access
Volume 425, Number 2, October II 2004
Page(s) 475 - 487
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20047156

A&A 425, 475-487 (2004)
DOI: 10.1051/0004-6361:20047156

QSO size ratios from multiband monitoring of a microlensing high-magnification event

L. J. Goicoechea1, V. Shalyapin1, 2, 3, J. González-Cadelo1 and A. Oscoz4

1  Departamento de Física Moderna, Universidad de Cantabria, Avda. de Los Castros s/n, 39005 Santander, Spain
    e-mail: goicol@unican.es; juan.gonzalezc@alumnos.unican.es
2  Institute of Radio Astronomy, NAS of Ukraine, 4 Krasnoznamennaya St., 61002, Kharkov, Ukraine
3  O. Ya. Usikov Institute of Radiophysics and Electronics, NAS of Ukraine, 12 Academician Proskura St., 61085, Kharkov, Ukraine
    e-mail: vshal@ire.kharkov.ua
4  Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38200 La Laguna, Spain
    e-mail: aoscoz@ll.iac.es

(Received 27 January 2004 / Accepted 16 June 2004)

We introduce a new scheme to study the nature of the central engine in a lensed QSO. The compact emission regions could have different sizes in different optical wavelengths, and our framework permits us to obtain the source size ratios when a microlensing special high-magnification event (e.g., a caustic crossing event, a two-dimensional maximum crossing event and so on) is produced in one of the QSO components. To infer the source size ratios, only cross-correlations between the brightness records in different optical bands are required. While the deconvolution method leads to richer information (1D intrinsic luminosity profiles), the new approach is free of the technical problems with complex inversion procedures. Using simulations related to recent VR data of Q2237+0305A, we discuss how well the scheme is able to determine the visible-to-red ratio q = RV/RR. We conclude that extremely accurate fluxes (with a few  $\mu$Jy uncertainties, or equivalently, a few milli-magnitudes errors) can lead to ~10% measurements of  q. Taking into account the errors in the fluxes of Q2237+0305A from a normal ground-based telescope, ~10  $\mu$Jy (~10 mmag), it must be possible to achieve smaller errors using current superb-telescopes, and thus, an accurate determination of  q. To measure the visible-to-red ratio, the light curves must not be contaminated by an intrinsic event or a large high-frequency intrinsic signal, i.e., exceeding the $\mu$Jy (mmag) level. For an arbitrary lensed QSO, the framework seems to work better with very fast microlensing events.

Key words: gravitational lensing -- galaxies: nuclei -- galaxies: quasars: general -- galaxies: quasars: individual: Q2237+0305

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© ESO 2004