Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f1.eps} \end{figure}$ Figure 1: Distribution of $\theta ^2$ for on-source events (points) and normalized off-source events (shaded) from observations of PG 1553+113. The dashed curve represents the $\theta ^2$ distribution expected for a point source of VHE $\gamma$ -rays at $40^{\circ }$ zenith angle with a photon index $\Gamma =4.46$ . The vertical line represents the cut on $\theta ^2$ applied to the data.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f2.eps} \end{figure}$ Figure 2: Overall VHE energy spectrum observed from PG 1553+113. The dashed line represents the best $\chi ^2$ fit of a power law to the observed data. The upper limits are at the 99% confidence level (Feldman & Cousins 1998). Only the statistical errors are shown.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f3.eps} \end{figure}$ Figure 3: Annual VHE energy spectra observed by HESS from PG 1553+113. Each line represents the best $\chi ^2$ fit of a power law to the observed data. Only the statistical errors are shown.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f4.eps} \end{figure}$ Figure 4: Integral flux, I(>300 GeV), measured by HESS from PG 1553+113 during each dark period of observations. The horizontal line represents the average flux for all the HESS observations. For each point the time-averaged $\Gamma =4.46$ is assumed. Only the statistical errors are shown.
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In the text

$\begin{figure} \par$\begin{array}{c@{\hspace{0.5cm}}c} \par\multicolumn{1}{l}{\m... ...0.0cm] \mbox{\bf (c)} & \mbox{\bf (d)} \\ [0.2cm] \par\end{array}$ \end{figure}$ Figure 5: Integral flux, I(>300 GeV), measured by HESS from PG 1553+113 during each night of observations. The plots a)- d), represent the April 2005, August 2005, April 2006 and July 2006 dark periods, respectively. The horizontal line represents the average flux for all the HESS observations. For each point the time-average $\Gamma =4.46$ is assumed. Only the statistical errors are shown.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f6.eps} \end{figure}$ Figure 6: Spectrum measured by HESS from PG 1553+113 in 2005 compared to the previously published version (Aharonian et al. 2006a). The integral flux above 300 GeV is three times higher. Only the statistical errors are shown.
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In the text

$\begin{figure} \par$\begin{array}{c@{\hspace{0.5cm}}c} \par\multicolumn{1}{l}{\m... ...\\ [0.0cm] \mbox{\bf (a)} & \mbox{\bf (b)} \\ [0.2cm] \end{array}$\end{figure}$ Figure 7: a) Spectrum observed by HESS from PG 1553+113 during observations in July 2006. The dashed line represents the best $\chi ^2$ fit of a power law to the observed data. The upper limits are at the 99% confidence level (Feldman & Cousins 1998). b) Integral flux, I(>300 GeV), measured by HESS from PG 1553+113 in each run taken during simultaneous Suzaku observations. The horizontal line represents the average flux for all the HESS observations. For each point in the light curve the time-average $\Gamma =4.46$ is assumed. For both plots, only the statistical errors are shown.
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{8603_f8.eps} \end{figure}$ Figure 8: Top: H+K-band spectrum of PG 1553+113 extracted from a 5-pixel radius aperture. The gap is due to the highly reduced atmospheric transmission between H and K bands. Bottom: telluric spectrum extracted from the standard stars.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f1.eps} \end{figure}$	Figure 1: Distribution of $\theta ^2$ for on-source events (points) and normalized off-source events (shaded) from observations of PG 1553+113. The dashed curve represents the $\theta ^2$ distribution expected for a point source of VHE $\gamma$ -rays at $40^{\circ }$ zenith angle with a photon index $\Gamma =4.46$ . The vertical line represents the cut on $\theta ^2$ applied to the data.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f2.eps} \end{figure}$	Figure 2: Overall VHE energy spectrum observed from PG 1553+113. The dashed line represents the best $\chi ^2$ fit of a power law to the observed data. The upper limits are at the 99% confidence level (Feldman & Cousins 1998). Only the statistical errors are shown.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f3.eps} \end{figure}$	Figure 3: Annual VHE energy spectra observed by HESS from PG 1553+113. Each line represents the best $\chi ^2$ fit of a power law to the observed data. Only the statistical errors are shown.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f4.eps} \end{figure}$	Figure 4: Integral flux, I(>300 GeV), measured by HESS from PG 1553+113 during each dark period of observations. The horizontal line represents the average flux for all the HESS observations. For each point the time-averaged $\Gamma =4.46$ is assumed. Only the statistical errors are shown.
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$\begin{figure} \par$\begin{array}{c@{\hspace{0.5cm}}c} \par\multicolumn{1}{l}{\m... ...0.0cm] \mbox{\bf (c)} & \mbox{\bf (d)} \\ [0.2cm] \par\end{array}$ \end{figure}$	Figure 5: Integral flux, I(>300 GeV), measured by HESS from PG 1553+113 during each night of observations. The plots a)- d), represent the April 2005, August 2005, April 2006 and July 2006 dark periods, respectively. The horizontal line represents the average flux for all the HESS observations. For each point the time-average $\Gamma =4.46$ is assumed. Only the statistical errors are shown.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8603_f6.eps} \end{figure}$	Figure 6: Spectrum measured by HESS from PG 1553+113 in 2005 compared to the previously published version (Aharonian et al. 2006a). The integral flux above 300 GeV is three times higher. Only the statistical errors are shown.
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$\begin{figure} \par\includegraphics[width=16.5cm,clip]{8603_f8.eps} \end{figure}$	Figure 8: Top: H+K-band spectrum of PG 1553+113 extracted from a 5-pixel radius aperture. The gap is due to the highly reduced atmospheric transmission between H and K bands. Bottom: telluric spectrum extracted from the standard stars.
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