All Figures

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg1a.eps}\h... ...*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg1b.eps} \end{figure}$ Figure 1: Steady proton ( left panel) and electron ( right panel) distributions in the innermost region of NGC 253.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg2a.eps}\h... ...*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg2b.eps} \end{figure}$ Figure 2: Left: ratio of the steady proton population in the surrounding disk to that in the innermost starburst region. Right: ratio between the steady proton distribution in the IS, when the gas density is artificially enhanced and diminished by a factor of 2.
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In the text

$\begin{figure} \par\includegraphics[width=6.7cm,height=7.6cm,clip]{3613fg3.eps} \end{figure}$ Figure 3: Steady population of primary-only and secondary-only electrons. Only the region of the secondary dominance of the distribution is shown.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg4a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg4b.eps} \end{figure}$ Figure 4: Left: multifrequency spectrum of NGC 253 from radio to IR, with the result of our modelling. The experimental data points correspond to: pentagons, Melo et al. (2002); diamonds, Telesco et al. (1980); down-facing triangles, Rieke et al. (1973); stars, Hildebrand et al. (1977); up-facing triangles, Elias et al. (1978); circles, Ott et al. (2005); squares, Carilli (1996). Right: IR flux from NGC 253 assuming a dilute blackbody with temperature $T_{\rm dust }= 50$ K and different total luminosities.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg5a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg5b.eps} \end{figure}$ Figure 5: Left: differential $\gamma$ -ray fluxes from the central region of NGC 253. Total contribution of the surrounding disk is shown separately, as are the EGRET upper limits. In the case of the IS, we show the relative contributions of bremsstrahlung, inverse Compton, and neutral pion decay to the $\gamma$ -ray flux separately. Right: integral $\gamma$ -ray fluxes. The EGRET upper limit (for energies above 100 MeV), the CANGAROO integral flux as estimated from their fit, and the HESS sensitivity (for a 5 $\sigma$ detection in 50 h) are given. Absorption effects are already taken into account. Also shown is the recently released HESS upper limit curve on NGC 253.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg6a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg6b.eps} \end{figure}$ Figure 6: Left: opacities to $\gamma$ -ray scape as a function of energy. The highest energy is dominated by $\gamma \gamma$ processes, whereas $\gamma Z$ dominates the opacity at low energies. Significant $\tau _{\rm max}$ are only encountered above 1 TeV. Right: modification of the $\gamma$ -ray spectrum introduced by the opacity to $\gamma$ -ray escape.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg7.eps} \end{figure}$ Figure 7: Proton distribution when different convective and the pp timescales are taken into account as compared with a (arbitrary) solution when $\tau (E)=\tau _D$ , i.e., diffusion only. Clearly, convection plus pp timescales dominates the spectrum.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg8a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg8b.eps} \end{figure}$ Figure 8: Left: energy density contained in the steady population of protons above the energy given by the x-axis. Right: cosmic ray enhancement factor obtained from the steady spectrum distribution in the innermost starburst nucleus of NGC 253.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg9.eps} \end{figure}$ Figure 9: Integral $\gamma$ -ray fluxes zoomed in the region above 100 GeV, together with the (2 telescopes) HESS upper limits and the (4 telescopes) HESS sensitivity.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f10a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f10b.eps} \end{figure}$ Figure 10: Comparing sum of diffractive and non-diffractive contributions Kamae et al. model A with Aharonian and Atoyan's formula for the total inelastic cross section.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f11.eps} \end{figure}$ Figure 11: Comparing $\gamma$ -ray emissivities within the $\delta$ -function approximation (Kamae et al.'s model A and Aharonian and Atoyan's formula for the inelastic cross section) with computations using differential cross section parameterizations.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f12a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f12b.eps} \end{figure}$ Figure 12: Left: comparing inclusive cross sections. Kamae et al.'s model A data comes from their Fig. 5. The Blattnig et al. curve is obtained from Eq. (9) and the experimental compilation is from Dermer (1986b). Right: $\gamma$ -ray emissivities as in Fig. 11 multiplied by E^2.75, with 2.75 being the slope of the proton primary spectrum.
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f13a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f13b.eps} \end{figure}$ Figure 13: Comparing inclusive cross sections for charged pions. Solid curves are obtained from Eqs. (30) and (31) of Blattnig et al. (2000b), and experimental compilation is from Dermer (1986b).
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In the text

$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg1a.eps}\h... ...*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg1b.eps} \end{figure}$	Figure 1: Steady proton ( left panel) and electron ( right panel) distributions in the innermost region of NGC 253.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg2a.eps}\h... ...*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg2b.eps} \end{figure}$	Figure 2: Left: ratio of the steady proton population in the surrounding disk to that in the innermost starburst region. Right: ratio between the steady proton distribution in the IS, when the gas density is artificially enhanced and diminished by a factor of 2.
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$\begin{figure} \par\includegraphics[width=6.7cm,height=7.6cm,clip]{3613fg3.eps} \end{figure}$	Figure 3: Steady population of primary-only and secondary-only electrons. Only the region of the secondary dominance of the distribution is shown.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg6a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg6b.eps} \end{figure}$	Figure 6: Left: opacities to $\gamma$ -ray scape as a function of energy. The highest energy is dominated by $\gamma \gamma$ processes, whereas $\gamma Z$ dominates the opacity at low energies. Significant $\tau _{\rm max}$ are only encountered above 1 TeV. Right: modification of the $\gamma$ -ray spectrum introduced by the opacity to $\gamma$ -ray escape.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg7.eps} \end{figure}$	Figure 7: Proton distribution when different convective and the pp timescales are taken into account as compared with a (arbitrary) solution when $\tau (E)=\tau _D$ , i.e., diffusion only. Clearly, convection plus pp timescales dominates the spectrum.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg8a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613fg8b.eps} \end{figure}$	Figure 8: Left: energy density contained in the steady population of protons above the energy given by the x-axis. Right: cosmic ray enhancement factor obtained from the steady spectrum distribution in the innermost starburst nucleus of NGC 253.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613fg9.eps} \end{figure}$	Figure 9: Integral $\gamma$ -ray fluxes zoomed in the region above 100 GeV, together with the (2 telescopes) HESS upper limits and the (4 telescopes) HESS sensitivity.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f10a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f10b.eps} \end{figure}$	Figure 10: Comparing sum of diffractive and non-diffractive contributions Kamae et al. model A with Aharonian and Atoyan's formula for the total inelastic cross section.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f11.eps} \end{figure}$	Figure 11: Comparing $\gamma$ -ray emissivities within the $\delta$ -function approximation (Kamae et al.'s model A and Aharonian and Atoyan's formula for the inelastic cross section) with computations using differential cross section parameterizations.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f12a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f12b.eps} \end{figure}$	Figure 12: Left: comparing inclusive cross sections. Kamae et al.'s model A data comes from their Fig. 5. The Blattnig et al. curve is obtained from Eq. (9) and the experimental compilation is from Dermer (1986b). Right: $\gamma$ -ray emissivities as in Fig. 11 multiplied by E^2.75, with 2.75 being the slope of the proton primary spectrum.
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$\begin{figure} \par\includegraphics[width=5.6cm,height=7cm,clip]{3613f13a.eps}\h... ...e*{4mm} \includegraphics[width=5.6cm,height=7cm,clip]{3613f13b.eps} \end{figure}$	Figure 13: Comparing inclusive cross sections for charged pions. Solid curves are obtained from Eqs. (30) and (31) of Blattnig et al. (2000b), and experimental compilation is from Dermer (1986b).
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