All Figures

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3983f1.eps} \end{figure}$ Figure 1: LECS+MECS 26-27 July spectrum of BL Lac. The spectrum is modeled with a power law and a fixed $N_{\rm H}= 2.5\times 10^{21}$ cm^-2. We choose this value to be consistent with previous work (Ravasio et al. 2002; Madejski et al. 1999; Sambruna et al. 1999).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{3983-f2.ps} \end{figure}$ Figure 2: LECS+MECS+PDS 31 October-2 November spectrum of BL Lac. Both a single and a broken power law model cannot reproduce the whole observed spectrum. PDS data lie above the power-law best fit of the of LECS+MECS spectrum. The LECS+MECS spectrum is well fitted by a convex broken power law.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm,clip]{3983-f3.ps} \end{figure}$ Figure 3: LECS 0.7-2 keV (top panel), MECS 2-10 keV (bottom panel) light curves of BL Lac during the July 2000 BeppoSAX observation. Note that in the LECS range the source displays larger variability than at higher energies.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm,clip]{3983-f4.ps} \end{figure}$ Figure 4: LECS 0.5-2 keV (top panel), MECS 2-4 keV (mid panel) and MECS 4-10 keV (bottom panel) light curves of BL Lac during the October-November 2000 BeppoSAX observation.
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In the text

$\begin{figure} \par\includegraphics[width=11cm,clip]{3983-f5.ps} \end{figure}$ Figure 5: Left panel: 26-27 July SED. Right panel: 31 October-2 November SED. The black butterflies represent RXTE simultaneous data. The HEGRA upper limit is calculated assuming a spectral energy index $\alpha _{\rm TeV}=1.5$ above 0.7 TeV. The optical slopes are calculated on the weigthed average UBVRI fluxes ( A_B=1.42). July fluxes (mJy): $<{F_{I}}>~=5.17\pm0.07; <F_{R}>~=8.12\pm0.01; <F_{V}>~=12.08\pm0.04; <F_{B}>~=16.54\pm0.02; <F_{U}>~=22.28\pm0.06$ . October fluxes (mJy): $<F_{I}>~=8.26\pm0.09; <F_{R}>~=11.96\pm0.05; <F_{V}>~=17.56\pm0.06; <F_{B}>~=22.43\pm0.08; <F_{U}>~=27.97\pm0.18$ .
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In the text

$\begin{figure} \par\includegraphics[width=10cm,clip]{3983-f6.ps} \end{figure}$ Figure 6: Simultaneous multiwavelength SEDs of BL Lac. Left-top panel: July and October-November 2000 SEDs ( BeppoSAX). We have reported optical data corrected for A_B=1.42, to be consistent with the other historical observations. Right-top panel: November 1995 (ASCA) and July 1997 (RXTE) SEDs. Left-bottom panel: June and December 1999 SEDs ( BeppoSAX). Right-bottom panel: June 1980 (Einstein), December 1983 (EXOSAT), June and July 1988 (GINGA) multiwavelength SEDs. The dotted butterfly represent the December 1982 ROSAT data.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{3983-f7.ps} \end{figure}$ Figure 7: Optical to X-ray SED of October-November 2000 BeppoSAX observation. Filled circles represent data corrected for A_B=1.42 corresponding to $N_{\rm H}= 2.5\times 10^{21}$ cm^-2. Filled triangles represent data corrected for $A_{B}=2.5\equiv N_{\rm H}=4.8\times 10^{21}$ cm^-2. Open circles represent raw optical data and optical data dereddened with A_B=4.2. The two stars represent the B and R-band data dereddened with A_B=1.42 and corrected for the host galaxy contribution. The two dotted lines represent the extrapolation of the BeppoSAX spectrum to the optical band and a parabolic curve which connects X-ray and optical data dereddened with A_B=2.5. See text for discussion.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{3983-f8.ps} \end{figure}$ Figure 8: LECS+MECS+PDS 31-October-2 November spectrum of BL Lac. fitted by the model in equation 9, using $\Gamma _1=1$ . If $\Gamma _1 \leq 1$ the data are badly fitted by this model.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3983f1.eps} \end{figure}$	Figure 1: LECS+MECS 26-27 July spectrum of BL Lac. The spectrum is modeled with a power law and a fixed $N_{\rm H}= 2.5\times 10^{21}$ cm^-2. We choose this value to be consistent with previous work (Ravasio et al. 2002; Madejski et al. 1999; Sambruna et al. 1999).
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$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{3983-f2.ps} \end{figure}$	Figure 2: LECS+MECS+PDS 31 October-2 November spectrum of BL Lac. Both a single and a broken power law model cannot reproduce the whole observed spectrum. PDS data lie above the power-law best fit of the of LECS+MECS spectrum. The LECS+MECS spectrum is well fitted by a convex broken power law.
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$\begin{figure} \par\includegraphics[width=7.2cm,clip]{3983-f3.ps} \end{figure}$	Figure 3: LECS 0.7-2 keV (top panel), MECS 2-10 keV (bottom panel) light curves of BL Lac during the July 2000 BeppoSAX observation. Note that in the LECS range the source displays larger variability than at higher energies.
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$\begin{figure} \par\includegraphics[width=7.2cm,clip]{3983-f4.ps} \end{figure}$	Figure 4: LECS 0.5-2 keV (top panel), MECS 2-4 keV (mid panel) and MECS 4-10 keV (bottom panel) light curves of BL Lac during the October-November 2000 BeppoSAX observation.
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$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{3983-f8.ps} \end{figure}$	Figure 8: LECS+MECS+PDS 31-October-2 November spectrum of BL Lac. fitted by the model in equation 9, using $\Gamma _1=1$ . If $\Gamma _1 \leq 1$ the data are badly fitted by this model.
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