All Figures

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{4010_f1.ps}\end{figure}$ Figure 1: The LECS (upper panel) and MECS (central panel) light curves of Mkn 421 during the observation of May 4-8, 1999. Data are binned in intervals of 5700 s, approximately corresponding to a BeppoSAX orbit. The vertical scale is the same in the two panels to show the different amplitudes of the intensity variations. In the lower panel the corresponding hardness ratio (HR) is plotted. The dashed vertical lines indicate the four time segments considered in the spectral analysis.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{4010_f2.ps}\end{figure}$ Figure 2: The LECS (upper panel) and MECS (central panel) light curves of Mkn 421 during the observation of April 26-May 3, 2000. In the lower panel the corresponding hardness ratio (HR) is plotted. MECS was not operating in the time interval from 360 000 to 480 000 s after the beginning of the observation. Only the data taken in the first 360 000 s (April 26-30) were used in the spectral analysis. Data are binned in intervals of 5700 s, approximately corresponding to a BeppoSAX orbit. The vertical scale of the two panels are equal to show better the different intensity variations.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{4010_f3.ps}\end{figure}$ Figure 3: The LECS (upper panel) and MECS (central panel) light curves of Mkn 421 during the observation of May 9-12, 2000. Data are binned in intervals of 5700 s, approximately corresponding to a BeppoSAX orbit. The vertical scale is the same in the two panels to show the different amplitudes of the intensity variations. In the lower panel the corresponding hardness ratio (HR) is plotted. The dashed vertical lines indicate the five time segments considered in the spectral analysis.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4010_f4.ps}\end{figure}$ Figure 4: The X-ray Spectral Energy Distributions of Mkn 421 in some of the BeppoSAX 1997-1998 observations deconvolved with a log-parabolic law. Dashed lines are the best fit to the observed data.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4010_f5.ps}\end{figure}$ Figure 5: The optical to X-ray Spectral Energy Distribution of Mkn 421 observed on 1998, April 23-24. Two log-parabolic spectral distributions for the optical and X-ray data sets are shown, together with possible power law extrapolations of X-ray data at optical frequencies. Notice that these extrapolations cannot match the photometric R, V, B points.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4010_f6a.ps}\vspace*{1cm} \includegraphics[width=8.8cm,clip]{4010_f6b.ps}\end{figure}$ Figure 6: Upper panel: best fit of the LECS and MECS data with a log-parabolic law of the 1999 BeppoSAX observation of Mkn 421 without gain correction. Note the large residuals of the LECS points between 0.2 and 0.6 keV due to some systematics due to the near Carbon edge.
Lower panel: best fit of the same data after the gain adjustment of the LECS. The spurious features at low energies practically disappeared.
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In the text

$\begin{figure} \par\includegraphics[width=11.35cm,clip]{4010_f7.ps}\end{figure}$ Figure 7: The X-ray Spectral Energy Distributions of Mkn 421 in the long BeppoSAX observations of May 1999, April and May 2000. Best fit spectra (dashed lines) were obtained with a log-parabolic law. The SED of the two observations of 1997, May 4 and 1998, April 21 are also plotted to show the spectral evolution of the source.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f8.ps}\end{figure}$ Figure 8: The Spectral Energy Distributions of Mkn 421 in the four time segments of the May 1999 observation. Dashed lines are the log-parabolic best fits, while the thick solid line is the best fit of the entire observation.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f9.ps}\end{figure}$ Figure 9: The Spectral Energy Distributions of Mkn 421 in the High and Faint states during the April 2000 observation. Dashed lines are the log-parabolic best fits, the thick solid line is the best fit of the entire May 1999 observation, the same plotted in Fig. 8, shown for a better comparison among the different luminosity states of the source.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f10.ps}\end{figure}$ Figure 10: The Spectral Energy Distributions of Mkn 421 in the first three time segments of the May 2000 observation. Dashed lines are the log-parabolic best fits. The thick solid line is the best fit of the entire May 1999 observation, the same plotted in Fig. 8, shown for a better comparison among the different luminosity states of the source.
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In the text

$\begin{figure} \par\includegraphics[width=7.3cm,clip]{4010_f11.ps}\end{figure}$ Figure 11: The high correlation between the two spectral parameters a and b of the log-parabolic law supports the energy dependent statistical acceleration of the emitting electrons.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4010_f4.ps}\end{figure}$	Figure 4: The X-ray Spectral Energy Distributions of Mkn 421 in some of the BeppoSAX 1997-1998 observations deconvolved with a log-parabolic law. Dashed lines are the best fit to the observed data.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{4010_f5.ps}\end{figure}$	Figure 5: The optical to X-ray Spectral Energy Distribution of Mkn 421 observed on 1998, April 23-24. Two log-parabolic spectral distributions for the optical and X-ray data sets are shown, together with possible power law extrapolations of X-ray data at optical frequencies. Notice that these extrapolations cannot match the photometric R, V, B points.
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$\begin{figure} \par\includegraphics[width=11.35cm,clip]{4010_f7.ps}\end{figure}$	Figure 7: The X-ray Spectral Energy Distributions of Mkn 421 in the long BeppoSAX observations of May 1999, April and May 2000. Best fit spectra (dashed lines) were obtained with a log-parabolic law. The SED of the two observations of 1997, May 4 and 1998, April 21 are also plotted to show the spectral evolution of the source.
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$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f8.ps}\end{figure}$	Figure 8: The Spectral Energy Distributions of Mkn 421 in the four time segments of the May 1999 observation. Dashed lines are the log-parabolic best fits, while the thick solid line is the best fit of the entire observation.
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$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f9.ps}\end{figure}$	Figure 9: The Spectral Energy Distributions of Mkn 421 in the High and Faint states during the April 2000 observation. Dashed lines are the log-parabolic best fits, the thick solid line is the best fit of the entire May 1999 observation, the same plotted in Fig. 8, shown for a better comparison among the different luminosity states of the source.
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$\begin{figure} \par\includegraphics[width=7.4cm,clip]{4010_f10.ps}\end{figure}$	Figure 10: The Spectral Energy Distributions of Mkn 421 in the first three time segments of the May 2000 observation. Dashed lines are the log-parabolic best fits. The thick solid line is the best fit of the entire May 1999 observation, the same plotted in Fig. 8, shown for a better comparison among the different luminosity states of the source.
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$\begin{figure} \par\includegraphics[width=7.3cm,clip]{4010_f11.ps}\end{figure}$	Figure 11: The high correlation between the two spectral parameters a and b of the log-parabolic law supports the energy dependent statistical acceleration of the emitting electrons.
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