All Figures

$\begin{figure} \par\includegraphics[width=17cm,clip]{0567fig1.eps} \end{figure}$ Figure 1: Comparison of the ACFs of 6 GRBs obtained using data from two different experiments. Solid lines: Konus 64 ms data in the 50-200 keV energy band; gray lines: BATSE 64 ms data in the 55-320 keV energy range. There is sufficiently good agreement for the bright bursts, when the results are not very sensitive to the background estimation. GRB 971214 is considerably dimmer than the others (see the text for discussion).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig2.eps} \end{figure}$ Figure 2: Two ACF functions of GRB 030329. Solid line: Konus 64 ms data in the 50-200 keV energy band; gray line: INTEGRAL 50 ms data with a soft low energy cut-off at $\sim$ 80 keV. The high secondary peak of the ACF reflects the two bright pulse structure of the light curve.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{0567fig3.eps} \end{figure}$ Figure 3: a) Autocorrelation functions of the 16 bursts sample. BATSE and Konus cases are shown in gray and solid lines respectively. b) Local ACFs, where time dilation due to cosmic effect has been corrected, being $\tau ' = \tau /(1+z)$ . GRB 980329 is shown with dashed lines assuming a redshift z=3.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig4.eps} \end{figure}$ Figure 4: Mean value of the local ACF for narrow and broad width bursts (solid lines). The $1 \sigma$ region about the mean is also shown (gray lines). At half-maximum $A(\tau ')=0.5$ , $\tau '=(1.6\pm 0.5)$ s and $\tau '=(7.5\pm 0.3)$ s for narrow and broad widths respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig5.eps} \end{figure}$ Figure 5: Correlation between the width at half-maximum $\tau _{0}$ and the dilation factor 1+z. Bursts are classified into narrow and broad width $\tau '_{0}$ cases, as seen by a local observer, and they are marked by squares and triangles respectively. GRB 980329 is indicated with a hollow square; its redshift is only known to be within the shown zrange. A linear fit of the form f(x)=a x gives $a_n=(1.42\pm 0.15)$ s and $a_b=(7.54\pm 0.10)$ s for narrow and broad sets. The slopes are approximately equal to the average $\tau '_{0}$ for each set. Note that since the slope ratio is 5.3, for a given $\tau _{0}$ each correlation predicts very different 1+z values.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig6.eps} \end{figure}$ Figure 6: Variation of the dispersion of the ACF width with additional redshift dependencies. The local values are calculated assuming $\tau '_{0} =\tau _{0}/(1+z)^{1+a}$ , where a is an unknown correction index. The left ordinate shows the relative dispersion of the broad ( dotted line) and narrow ( dashed line) sets. Dispersion minima occur at $a \ll 1$ in both cases. The right ordinate shows for the solid line the difference between the mean values of each set ( $\mu _b$ , $\mu _n$ ) in number of total standard deviations ( $\sigma _b+\sigma _n$ ). The gap between sets remains above $3\sigma$ over a large range ( -0.4<a<0.3), indicating the robustness of the bimodality result to additional corrections.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig7.eps} \end{figure}$ Figure 7: Distribution of the ACF width at half-maximum for a sample of 170 BATSE GRBs. Dashed-line: logarithmic histogram of the width $\tau _{0}$ (in seconds). The distribution seems unimodal. Solid-line: The width corrected for cosmic time dilation $\tau '_{0}$ , using estimated redshifts derived from the luminosity-variability correlation (Fenimore & Ramirez-Ruiz 2000). The distribution appears now bimodal, with median values approximately 0.7 s and 4.0 s for each subset.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig2.eps} \end{figure}$	Figure 2: Two ACF functions of GRB 030329. Solid line: Konus 64 ms data in the 50-200 keV energy band; gray line: INTEGRAL 50 ms data with a soft low energy cut-off at $\sim$ 80 keV. The high secondary peak of the ACF reflects the two bright pulse structure of the light curve.
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$\begin{figure} \par\includegraphics[width=17cm,clip]{0567fig3.eps} \end{figure}$	Figure 3: a) Autocorrelation functions of the 16 bursts sample. BATSE and Konus cases are shown in gray and solid lines respectively. b) Local ACFs, where time dilation due to cosmic effect has been corrected, being $\tau ' = \tau /(1+z)$ . GRB 980329 is shown with dashed lines assuming a redshift z=3.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0567fig4.eps} \end{figure}$	Figure 4: Mean value of the local ACF for narrow and broad width bursts (solid lines). The $1 \sigma$ region about the mean is also shown (gray lines). At half-maximum $A(\tau ')=0.5$ , $\tau '=(1.6\pm 0.5)$ s and $\tau '=(7.5\pm 0.3)$ s for narrow and broad widths respectively.
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