EDP Sciences
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Issue A&A
Volume 480, Number 2, March III 2008
Page(s) 327 - 334
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20078221

A&A 480, 327-334 (2008)
DOI: 10.1051/0004-6361:20078221

The multiple quasar Q2237+0305 under a microlensing caustic

T. Anguita1, R. W. Schmidt1, E. L. Turner2, J. Wambsganss1, R. L. Webster3, K. A. Loomis4, D. Long4, and R. McMillan4

1  Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
    e-mail: tanguita@ari.uni-heidelberg.de
2  Princeton University Observatory, Peyton Hall, Princeton, NJ 08544, USA
3  School of Physics, The University of Melbourne, Parkville, Victoria 3052, Australia
4  Apache Point Observatory, 2001 Apache Point Rd, Sunspot NM 88349, USA

(Received 4 July 2007 / Accepted 22 November 2007)

We use the high magnification event seen in the 1999 OGLE campaign light curve of image C of the quadruply imaged gravitational lens Q2237+0305 to study the structure of the quasar engine. We have obtained g'- and r'-band photometry at the Apache Point Observatory 3.5 m telescope where we find that the event has a smaller amplitude in the r'-band than in the g'- and OGLE V-bands. By comparing the light curves with microlensing simulations we obtain constraints on the sizes of the quasar regions contributing to the g'- and r'-band flux. Assuming that most of the surface mass density in the central kiloparsec of the lensing galaxy is due to stars and by modeling the source with a Gaussian profile, we obtain for the Gaussian width 1.20$\times$1015 $\sqrt{{M}/{0.1~M_\odot}}$ cm $\la \sigma_{g'} \la$ 7.96$\times$ 10 $^{15}
\sqrt{{M}/{0.1~M_\odot}}$ cm, where M is the mean microlensing mass, and a ratio $\sigma_{r'}/\sigma_{g'} = 1.25^{+0.45}_{-0.15}$. With the limits on the velocity of the lensing galaxy from Gil-Merino et al. (2005) as our only prior, we obtain 0.60$\times$1015 $\sqrt{{M}/{0.1~M_\odot}}$ cm $\la \sigma_{g'} \la$ 1.57$\times$1015 $\sqrt{{M}/{0.1~M_\odot}}$ cm and a ratio $\sigma_{r'}/\sigma_{g'} = 1.45^{+0.90}_{-0.25}$ (all values at 68 percent confidence). Additionally, from our microlensing simulations we find that, during the chromatic microlensing event observed, the continuum emitting region of the quasar crossed a caustic at $\geq$72 percent confidence.

Key words: gravitational lensing -- galaxies: quasars: individual: Q2237+0305 -- cosmology: observations -- accretion, accretion disks

© ESO 2008

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Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: N. Aghanim

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

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