Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=6cm,clip]{3254f1.eps} \end{figure}$ Figure 1: Pixel arrangement of the CANGAROO-II camera. The thick Box (1.84 $^\circ ~\times~$ 1.84 $^\circ$ ) is the trigger region. The camera consists of 36 boxes. Each box contains 16 PMTs, each 1/2 $^{\prime \prime }$ in diameter. In total, 552 PMTs are installed. Each pixel subtends 0.115 $^\circ ~\times~$ 0.115 $^\circ$ , defined by the light guide.
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In the text

$\begin{figure} \par\includegraphics[width=6.5cm,clip]{3254f2.eps} \end{figure}$ Figure 2: Scaler distribution: a) 2000-data and b) 2001-data, where "N'' denotes the number of hits per scaler count (horizontal axis). The rate at which each pixel exceeds the $\sim$ 2.5 p.e. threshold was monitored for 700 $\mu$ s each second.
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{3254f3.eps} \end{figure}$ Figure 3: ADC distribution for pixels, after pedestal levels had been subtracted, where "N'' denotes the number of hits per 10-ADC count. The small peak in negative region is due to the electronics undershoot.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f4.eps} \end{figure}$ Figure 4: TDC distributions: a) for all pixels, b) for pixels which satisfy t3a-clustering and do not satisfy t4a, and c) for pixels which satisfy t4a-clustering and do not satisfy t5a. "N'' denotes the number of hits per TDC count, which were normalized to 1 nsec. The horizontal axis is the TDC count.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f5.eps} \end{figure}$ Figure 5: Shower rates: a) hardware trigger rate; b) shower rate for events satisfying t3a-clustering, but not satisfying t4a; c) shower rate for events satisfying t4a-clustering, but not satisfying t5a; and d) shower rate for t4a-clustering. The vertical axis "N'' denotes the number of events per 5 min. The horizontal axis is the time in minutes from the start of the observation.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{3254f6.eps} \end{figure}$ Figure 6: Shower rate under a) good conditions and c) poor conditions. The horizontal axis is the time (minutes) from the start of an observation. The vertical axis ("N'') is the number of events per 5 min. The histogram is the shower rate, and the dashed line is the cut position, i.e., 600 events per 5 min were required for the data to be accepted. Plots b) and d) are the elevation angle distributions versus time. Data was accepted above an elevation angle of 70 $^\circ$ .
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f7.eps} \end{figure}$ Figure 7: Shower rates versus the cosine of the zenith angle.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f8.eps} \end{figure}$ Figure 8: Zenith-angle distribution after event selection. The vertical axis is the observation time in minutes. The mean is 11.1 $^\circ$ .
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In the text

$\begin{figure} \par\includegraphics[width=6.2cm,clip]{3254f9.eps} \end{figure}$ Figure 9: Distribution of energies for accepted events from theMonte-Carlo gamma-ray simulation; the solid line was obtained for a E^-2.5 spectrum and the dashed line for a E^-3.0 spectrum.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3254f10.eps} \end{figure}$ Figure 10: Image parameter distributions. The blank histograms were obtained from OFF-source observations. The hatched areas are the distributions for gamma-rays from our Monte-Carlo simulations.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f11.eps} \end{figure}$ Figure 11: $E_{{\rm ratio}}$ : ratio between the ADC counts of the maximum energy cluster and that of the remaining clusters. "N'' denotes the number of events. The blank histogram was obtained from an OFF-source run and the hatched histogram from the gamma-ray simulations.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f12.eps} \end{figure}$ Figure 12: Correlation between the Width and the logarithm of total ADC counts obtained from the gamma-ray simulations.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f13.eps} \end{figure}$ Figure 13: Likelihood distribution: a) for 2000 data and b) for 2001 data. "N'' denotes the number of events. The blank histograms are OFF-source data and the hatched areas are from the gamma-ray simulations.
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In the text

$\begin{figure} \par\includegraphics[width=5.9cm,clip]{3254f14.eps} \end{figure}$ Figure 14: FOM (figure of merit) vs. Likelihood-ratio cut for the combined-data is shown by the solid line. Also shown is the acceptance vs. Likelihood-ratio cut (the dashed line).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f15.eps} \end{figure}$ Figure 15: The distributions of $\alpha$ obtained for a) 2000 data and b) 2001 data. The points with error bars were obtained from ON-source data. The shaded histogram is from the OFF-source data.
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In the text

$\begin{figure} \par\includegraphics[width=5.2cm,clip]{3254f16ab.eps}\hspace*{1cm} \includegraphics[width=2.4cm,clip]{3254f16c.eps} \end{figure}$ Figure 16: $\alpha$ distributions obtained with a) the loose cut (L > 0.4), b) a tighter cut (L > 0.6), and c) "standard'' cuts. The points with error bars were obtained from ON-source data. The shaded histogram represents OFF-source data.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3254f17.eps}\end{figure}$ Figure 17: Effective area versus energy; a) effective areas after the pre-selection (the black squares), those after the distance cut (the black triangles), those after the Likelihood-ratio cut (the blank circles), and those with $\alpha < 15^{\rm o}$ (the blank squares). The effective area for the Whipple telescope is shown by the line (after the distance cut). b)The effective areas multiplied by E^-2.5 are shown in order to indicatethe threshold of the CANGAROO telescope.
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In the text

$\begin{figure} \par\includegraphics[width=6.6cm,clip]{3254f18.eps} \end{figure}$ Figure 18: Results of the Crab analysis. The differential flux obtained for the Crab nebula is shown in b), together with previous observations. The points with error bars were obtained by this experiment. The dotted line is the HEGRA result and the dashed line is the CANGAROO-I result. The insert a) is the $\alpha$ distribution. The points with error bars are obtained from ON-source data and the histogram is from OFF-source data. The lower plot c) is a significance map. The 65%-contour is drawn with the our estimated angular resolution (the arrows: $\pm 1 \sigma$ ).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f19.eps} \end{figure}$ Figure 19: Excesses versus observation times (after cloud cut) for all runs. The blank marks were obtained by an OFF-source run, and the filled marks by ON-source runs. The dashed line is the average flux.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f20.eps} \end{figure}$ Figure 20: Differential fluxes for the 2000 and 2001 data. The blank squares represent data from 2000, and the filled squares are from the 2001 data. The triangles are the upper limits. The dotted line is that of Crab nebula for a reference.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f21.eps} \end{figure}$ Figure 21: ADC threshold dependence of the differential fluxes.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f22.eps} \end{figure}$ Figure 22: Differential fluxes based on various assumptions concerning the Likelihood-ratios.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f23.eps} \end{figure}$ Figure 23: Differential flux estimated by the various energy spectra inputs in the Monte-Carlo simulation. The blank squares were obtained by E^-2.5, the black squares by E^-3.75, and the black circles by the exponential cutoff function described in the text.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f24.eps} \end{figure}$ Figure 24: Combined differential fluxes. The dotted line is that of Crab nebula observations. The other lines are the fitting results. The dashed line is that of a power-law. The solid curve is that with an exponential cutoff.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f25.eps} \end{figure}$ Figure 25: Significance map obtained by this experiment, shown by the thick contours. The thin contours are optical image by DSS2.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f26.eps} \end{figure}$ Figure 26: Efficiency versus offset angle of the gamma-ray source position from the center of the field of view.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f27.eps} \end{figure}$ Figure 27: Signal yield as a function of the upper range of the Distance cut. The yield was normalized to the total excess. The points with error bars were obtained by this experiment. The solid line was obtained from a Monte-Carlo simulation with a point source assumption. The dashed line is the case for a "diffusion angle'' of 0.4 $^\circ$ .
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In the text

$\begin{figure} \par\includegraphics[width=6cm,clip]{3254f1.eps} \end{figure}$	Figure 1: Pixel arrangement of the CANGAROO-II camera. The thick Box (1.84 $^\circ ~\times~$ 1.84 $^\circ$ ) is the trigger region. The camera consists of 36 boxes. Each box contains 16 PMTs, each 1/2 $^{\prime \prime }$ in diameter. In total, 552 PMTs are installed. Each pixel subtends 0.115 $^\circ ~\times~$ 0.115 $^\circ$ , defined by the light guide.
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$\begin{figure} \par\includegraphics[width=6.5cm,clip]{3254f2.eps} \end{figure}$	Figure 2: Scaler distribution: a) 2000-data and b) 2001-data, where "N'' denotes the number of hits per scaler count (horizontal axis). The rate at which each pixel exceeds the $\sim$ 2.5 p.e. threshold was monitored for 700 $\mu$ s each second.
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{3254f3.eps} \end{figure}$	Figure 3: ADC distribution for pixels, after pedestal levels had been subtracted, where "N'' denotes the number of hits per 10-ADC count. The small peak in negative region is due to the electronics undershoot.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f4.eps} \end{figure}$	Figure 4: TDC distributions: a) for all pixels, b) for pixels which satisfy t3a-clustering and do not satisfy t4a, and c) for pixels which satisfy t4a-clustering and do not satisfy t5a. "N'' denotes the number of hits per TDC count, which were normalized to 1 nsec. The horizontal axis is the TDC count.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f5.eps} \end{figure}$	Figure 5: Shower rates: a) hardware trigger rate; b) shower rate for events satisfying t3a-clustering, but not satisfying t4a; c) shower rate for events satisfying t4a-clustering, but not satisfying t5a; and d) shower rate for t4a-clustering. The vertical axis "N'' denotes the number of events per 5 min. The horizontal axis is the time in minutes from the start of the observation.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f7.eps} \end{figure}$	Figure 7: Shower rates versus the cosine of the zenith angle.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f8.eps} \end{figure}$	Figure 8: Zenith-angle distribution after event selection. The vertical axis is the observation time in minutes. The mean is 11.1 $^\circ$ .
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$\begin{figure} \par\includegraphics[width=6.2cm,clip]{3254f9.eps} \end{figure}$	Figure 9: Distribution of energies for accepted events from theMonte-Carlo gamma-ray simulation; the solid line was obtained for a E^-2.5 spectrum and the dashed line for a E^-3.0 spectrum.
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$\begin{figure} \par\includegraphics[width=7.4cm,clip]{3254f10.eps} \end{figure}$	Figure 10: Image parameter distributions. The blank histograms were obtained from OFF-source observations. The hatched areas are the distributions for gamma-rays from our Monte-Carlo simulations.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f11.eps} \end{figure}$	Figure 11: $E_{{\rm ratio}}$ : ratio between the ADC counts of the maximum energy cluster and that of the remaining clusters. "N'' denotes the number of events. The blank histogram was obtained from an OFF-source run and the hatched histogram from the gamma-ray simulations.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f12.eps} \end{figure}$	Figure 12: Correlation between the Width and the logarithm of total ADC counts obtained from the gamma-ray simulations.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f13.eps} \end{figure}$	Figure 13: Likelihood distribution: a) for 2000 data and b) for 2001 data. "N'' denotes the number of events. The blank histograms are OFF-source data and the hatched areas are from the gamma-ray simulations.
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$\begin{figure} \par\includegraphics[width=5.9cm,clip]{3254f14.eps} \end{figure}$	Figure 14: FOM (figure of merit) vs. Likelihood-ratio cut for the combined-data is shown by the solid line. Also shown is the acceptance vs. Likelihood-ratio cut (the dashed line).
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f15.eps} \end{figure}$	Figure 15: The distributions of $\alpha$ obtained for a) 2000 data and b) 2001 data. The points with error bars were obtained from ON-source data. The shaded histogram is from the OFF-source data.
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$\begin{figure} \par\includegraphics[width=5.2cm,clip]{3254f16ab.eps}\hspace*{1cm} \includegraphics[width=2.4cm,clip]{3254f16c.eps} \end{figure}$	Figure 16: $\alpha$ distributions obtained with a) the loose cut (L > 0.4), b) a tighter cut (L > 0.6), and c) "standard'' cuts. The points with error bars were obtained from ON-source data. The shaded histogram represents OFF-source data.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f19.eps} \end{figure}$	Figure 19: Excesses versus observation times (after cloud cut) for all runs. The blank marks were obtained by an OFF-source run, and the filled marks by ON-source runs. The dashed line is the average flux.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f20.eps} \end{figure}$	Figure 20: Differential fluxes for the 2000 and 2001 data. The blank squares represent data from 2000, and the filled squares are from the 2001 data. The triangles are the upper limits. The dotted line is that of Crab nebula for a reference.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f21.eps} \end{figure}$	Figure 21: ADC threshold dependence of the differential fluxes.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f22.eps} \end{figure}$	Figure 22: Differential fluxes based on various assumptions concerning the Likelihood-ratios.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f23.eps} \end{figure}$	Figure 23: Differential flux estimated by the various energy spectra inputs in the Monte-Carlo simulation. The blank squares were obtained by E^-2.5, the black squares by E^-3.75, and the black circles by the exponential cutoff function described in the text.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f24.eps} \end{figure}$	Figure 24: Combined differential fluxes. The dotted line is that of Crab nebula observations. The other lines are the fitting results. The dashed line is that of a power-law. The solid curve is that with an exponential cutoff.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f25.eps} \end{figure}$	Figure 25: Significance map obtained by this experiment, shown by the thick contours. The thin contours are optical image by DSS2.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f26.eps} \end{figure}$	Figure 26: Efficiency versus offset angle of the gamma-ray source position from the center of the field of view.
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$\begin{figure} \par\includegraphics[width=7cm,clip]{3254f27.eps} \end{figure}$	Figure 27: Signal yield as a function of the upper range of the Distance cut. The yield was normalized to the total excess. The points with error bars were obtained by this experiment. The solid line was obtained from a Monte-Carlo simulation with a point source assumption. The dashed line is the case for a "diffusion angle'' of 0.4 $^\circ$ .
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