All Figures

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[110pt,368pt][540pt,698pt]{3251.f1.ps}}\end{figure}$ Figure 1: Low energy spectral index distribution from Ghirlanda et al. (2002). The vertical lines represent the limits of the emission models reported in Table 1 and plotted in Fig. 2. The triangles represent the maximum values found from the spectral analysis of the bursts presented in this work along with their 90% confidence interval (horizontal bars). The gray histogram shows the distribution of the low energy spectral index found from the time resolved spectral analysis of the bursts presented in the text.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[90pt, 370pt][534pt,697pt]{3251.f2.ps}}\end{figure}$ Figure 2: Low energy spectral limits for different emission models (see Table 1). Examples of the BAND (solid line) and COMP model (dot-dashed line) with the low energy photon spectral index fixed at -1 (i.e. $EF_{E}\propto E^{1}$ ) are also represented for comparison.
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In the text

$\begin{figure} \par\resizebox{7.5cm}{!}{\includegraphics{3251.f3.ps}}\end{figure}$ Figure 3: Light curve and best fit parameters for GRB 980306. Top panel: light curve on the 64 ms timescale, integrated in the range 110-320 keV and summed over all triggered detectors. Mid panel: low energy power law spectral index ( $\alpha$ ). Horizontal lines mark the limits $\alpha =-2/3$ ( dot-dashed) and $\alpha =0$ ( dashed). Bottom panel: peak energy $E_{\rm peak}$ of the EF_Espectrum. Error bars represent the 90% confidence intervals on the best fit parameters. The filled circles indicate the spectra which have been fitted also with a black body model (see Table 2 and Sect. 4.5).
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In the text

$\begin{figure} \par\resizebox{7.8cm}{16cm}{\includegraphics{3251.f4.ps}}\end{figure}$ Figure 4: The light curve and time evolution of the best fit parameters of the BAND model for GRB 911118. Top panel: light curve on the 64 ms timescale in the energy range 110-320 keV, summed over all the triggered detectors. The vertical dotted lines represent the boundaries of the phases in which the spectrum is harder than E⁰ (phase A) and E^-2/3 (phase B). Mid panel: low energy power law spectral index $\alpha$ , with the limits at $\alpha =-2/3$ ( dot-dashed) and $\alpha =0$ ( dashed). Bottom panel: peak energy of the EF_E spectrum. The filled circles represent the spectra which have been fitted also with a blackbody model (see Table 2 and Sect. 4.5).
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[80,367][540,704]{3251.f5.ps}}\end{figure}$ Figure 5: Reduced $\chi ^{2}_{ r}$ (for typical 110 d.o.f.) of the fits with different models to the spectra of GRB 911118: BAND model (asterisks), BAND model with the low energy spectral index fixed at -2/3 (triangles).
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In the text

$\begin{figure} \par\resizebox{8.3cm}{!}{\includegraphics{3251.f6.ps}}\end{figure}$ Figure 6: GRB 911118 - slope of the power law fitted to the ratio between the observed time resolved spectra and the template spectra (simulated with $\alpha =0$ and $E_{\rm break}=E_{0}(fit))$ . Labels A and B refer to the two phases of GRB 911118 (Fig. 4) and the horizontal dotted line is the slope of the reference spectrum.
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In the text

$\begin{figure} \par\resizebox{8.1cm}{!}{\includegraphics{3251.f7.ps}} \par\end{figure}$ Figure 7: As Fig. 6 for GRB 980306.
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In the text

$\begin{figure} \par\resizebox{8.3cm}{16cm}{\includegraphics{3251.f8.ps}}\end{figure}$ Figure 8: GRB 910807 spectral evolution. Same as Fig. 3.
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In the text

$\begin{figure} \par\resizebox{17.5cm}{17cm}{\includegraphics[120pt,295pt][535pt,590pt] {3251.f9.ps}}\end{figure}$ Figure 9: Examples of black body fits for GRB 980306 (see Table 2). The integration times are indicated for each plot. The data-to-model ratios are reported in the bottom panels.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[40,162][550,714]{3251.f10.ps}}\end{figure}$ Figure 10: Total flux (top panel) and black body temperature (bottom panel) as a function of time for the spectra reported in Table 2 and considered acceptable in terms of residuals. The dashed lines in the bottom panel correspond to $T_{\rm BB}\propto t^{-1/4}$ .
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[90pt, 370pt][534pt,697pt]{3251.f2.ps}}\end{figure}$	Figure 2: Low energy spectral limits for different emission models (see Table 1). Examples of the BAND (solid line) and COMP model (dot-dashed line) with the low energy photon spectral index fixed at -1 (i.e. $EF_{E}\propto E^{1}$ ) are also represented for comparison.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[80,367][540,704]{3251.f5.ps}}\end{figure}$	Figure 5: Reduced $\chi ^{2}_{ r}$ (for typical 110 d.o.f.) of the fits with different models to the spectra of GRB 911118: BAND model (asterisks), BAND model with the low energy spectral index fixed at -2/3 (triangles).
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$\begin{figure} \par\resizebox{8.3cm}{!}{\includegraphics{3251.f6.ps}}\end{figure}$	Figure 6: GRB 911118 - slope of the power law fitted to the ratio between the observed time resolved spectra and the template spectra (simulated with $\alpha =0$ and $E_{\rm break}=E_{0}(fit))$ . Labels A and B refer to the two phases of GRB 911118 (Fig. 4) and the horizontal dotted line is the slope of the reference spectrum.
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$\begin{figure} \par\resizebox{8.1cm}{!}{\includegraphics{3251.f7.ps}} \par\end{figure}$	Figure 7: As Fig. 6 for GRB 980306.
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$\begin{figure} \par\resizebox{8.3cm}{16cm}{\includegraphics{3251.f8.ps}}\end{figure}$	Figure 8: GRB 910807 spectral evolution. Same as Fig. 3.
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$\begin{figure} \par\resizebox{17.5cm}{17cm}{\includegraphics[120pt,295pt][535pt,590pt] {3251.f9.ps}}\end{figure}$	Figure 9: Examples of black body fits for GRB 980306 (see Table 2). The integration times are indicated for each plot. The data-to-model ratios are reported in the bottom panels.
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$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[40,162][550,714]{3251.f10.ps}}\end{figure}$	Figure 10: Total flux (top panel) and black body temperature (bottom panel) as a function of time for the spectra reported in Table 2 and considered acceptable in terms of residuals. The dashed lines in the bottom panel correspond to $T_{\rm BB}\propto t^{-1/4}$ .
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