All Figures

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{2567f1.eps} % \end{figure}$ Figure 1: $\it UBVRI$ light curves of AO 0235+16 during the observing season 2003-2004; the XMM-Newton pointing of January 18-19 is marked by the vertical (cyan) line at JD = 2 453 023. The ELISA contribution has been subtracted as explained in the text.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f2.eps} \end{figure}$ Figure 2: $\it JHK$ light curves of AO 0235+16 during the 2003-2004 observing season compared to the ELISA-subtracted R-band one ( top). NIR data from Campo Imperatore are shown by (blue) circles, while (red) triangles indicate NIR data from the NOT.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f3.eps} \end{figure}$ Figure 3: R-band light curve of AO 0235+16 during November 10-14, 2001; data acquired with the 215 cm telescope of the CASLEO, Argentina.
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In the text

$\begin{figure} \par\includegraphics[width=12.9cm,clip]{2567f4.eps} % \end{figure}$ Figure 4: ELISA-subtracted R-band magnitudes of AO 0235+16 ( top) and radio fluxes (Jy) at different frequencies during the WEBT campaign. The vertical (cyan) line marks the XMM-Newton pointing of January 18-19, 2004. The dotted horizontal line at $F_\nu=1.5~\rm Jy$ is drawn to guide the eye through the flux variations.
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In the text

$\begin{figure} \par\includegraphics[width=12.9cm,clip]{2567f5.eps} % \end{figure}$ Figure 5: ELISA-subtracted R-band magnitudes of AO 0235+16 ( top) compared with radio fluxes (Jy) at different frequencies; in each panel the first (red) vertical line marks the last data published by Raiteri et al. (2001); the second (green) line indicates the start of the WEBT campaign, and the third (cyan) one corresponds to the XMM-Newton pointing of January 18-19, 2004.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.8cm,clip]{2567f6.eps} \end{figure}$ Figure 6: Spectra from the three EPIC detectors ( top) and ratio between data and folded model ( bottom) when fitting the data with a power-law model with Galactic absorption plus absorption by the foreground galaxy at z=0.524. The green, black, and red points refer to the pn, MOS1, and MOS2 detectors, respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f7.eps} \end{figure}$ Figure 7: Radio light curves at $\lambda$ 2.8 cm ( top) and $\lambda$ 6 cm ( bottom) obtained with the 100 m radio telescope at Effelsberg on January 18, 2004. The vertical line marks the start of the XMM-Newtonobservations.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f8.eps} \end{figure}$ Figure 8: $\it UBVRI$ light curves obtained at Mt. Maidanak (blue circles) and at La Palma by the NOT (red triangles) and by the KVA (green triangles) on January 18, 2004. The vertical line marks the start of the XMM-Newton observations.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f9.eps} \end{figure}$ Figure 9: The amount of absorption (mag) towards AO 0235+16 as a function of wavelength. The "NED'' case is compared with the "Jun'' one (see text); in this latter case, the total contribution is shown (red, solid line), together with the single contributions by the Milky Way (green, dashed-dotted) and by the z=0.524 foreground galaxy (blue, dashed). The yellow area indicates the wavelength region where the Junkkarinen et al. (2004) prescriptions are believed to give a good evaluation of the extinction.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f10.eps} \end{figure}$ Figure 10: Spectral energy distribution of AO 0235+16 in the optical-UV frequency range during the XMM-Newton pointing of January 18-19, 2004. Empty and filled circles indicate $\it IRVBU$ data from the NOT simultaneous with the XMM-Newton observations; triangles refer to the data from the XMM-Newton Optical Monitor (OM). Empty symbols represent data obtained according to the "NED'' case for the Galactic extinction; filled symbols refer to the "Jun'' case for the Galactic as well as the z=0.524 absorptions. The asterisk corresponds to a "corrected'' "Jun'' case (see text).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f11.eps} \end{figure}$ Figure 11: Broad-band spectral energy distribution of AO 0235+16 during the XMM-Newton pointing of January 18-19, 2004. Filled symbols indicate simultaneous data (see text for details).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f12.eps} \end{figure}$ Figure 12: Discrete correlation function (DFC) between the R-band and 8 GHz light curves. Two major peaks are visible, corresponding to time lags of 0 and 60 days.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{2567f1.eps} % \end{figure}$	Figure 1: $\it UBVRI$ light curves of AO 0235+16 during the observing season 2003-2004; the XMM-Newton pointing of January 18-19 is marked by the vertical (cyan) line at JD = 2 453 023. The ELISA contribution has been subtracted as explained in the text.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f2.eps} \end{figure}$	Figure 2: $\it JHK$ light curves of AO 0235+16 during the 2003-2004 observing season compared to the ELISA-subtracted R-band one ( top). NIR data from Campo Imperatore are shown by (blue) circles, while (red) triangles indicate NIR data from the NOT.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f3.eps} \end{figure}$	Figure 3: R-band light curve of AO 0235+16 during November 10-14, 2001; data acquired with the 215 cm telescope of the CASLEO, Argentina.
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$\begin{figure} \par\includegraphics[width=12.9cm,clip]{2567f4.eps} % \end{figure}$	Figure 4: ELISA-subtracted R-band magnitudes of AO 0235+16 ( top) and radio fluxes (Jy) at different frequencies during the WEBT campaign. The vertical (cyan) line marks the XMM-Newton pointing of January 18-19, 2004. The dotted horizontal line at $F_\nu=1.5~\rm Jy$ is drawn to guide the eye through the flux variations.
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$\begin{figure} \par\includegraphics[width=12.9cm,clip]{2567f5.eps} % \end{figure}$	Figure 5: ELISA-subtracted R-band magnitudes of AO 0235+16 ( top) compared with radio fluxes (Jy) at different frequencies; in each panel the first (red) vertical line marks the last data published by Raiteri et al. (2001); the second (green) line indicates the start of the WEBT campaign, and the third (cyan) one corresponds to the XMM-Newton pointing of January 18-19, 2004.
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$\begin{figure} \par\includegraphics[angle=-90,width=8.8cm,clip]{2567f6.eps} \end{figure}$	Figure 6: Spectra from the three EPIC detectors ( top) and ratio between data and folded model ( bottom) when fitting the data with a power-law model with Galactic absorption plus absorption by the foreground galaxy at z=0.524. The green, black, and red points refer to the pn, MOS1, and MOS2 detectors, respectively.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f7.eps} \end{figure}$	Figure 7: Radio light curves at $\lambda$ 2.8 cm ( top) and $\lambda$ 6 cm ( bottom) obtained with the 100 m radio telescope at Effelsberg on January 18, 2004. The vertical line marks the start of the XMM-Newtonobservations.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f8.eps} \end{figure}$	Figure 8: $\it UBVRI$ light curves obtained at Mt. Maidanak (blue circles) and at La Palma by the NOT (red triangles) and by the KVA (green triangles) on January 18, 2004. The vertical line marks the start of the XMM-Newton observations.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f11.eps} \end{figure}$	Figure 11: Broad-band spectral energy distribution of AO 0235+16 during the XMM-Newton pointing of January 18-19, 2004. Filled symbols indicate simultaneous data (see text for details).
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2567f12.eps} \end{figure}$	Figure 12: Discrete correlation function (DFC) between the R-band and 8 GHz light curves. Two major peaks are visible, corresponding to time lags of 0 and 60 days.
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