Changeset 6834 for trunk


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03/16/05 15:11:15 (20 years ago)
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hbartko
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  • trunk/MagicSoft/GC-Proposal/GC.tex

    r6833 r6834  
    7373\begin{itemize}
    7474\item to measure the gamma-ray flux and its energy dependence (due to the high
    75 zenith angles higher energies are accessible),
     75zenith angles higher energies up to about 20 TeV are accessible),
    7676\item to inter-calibrate MAGIC and HESS,
    7777\item to help resolving the flux discrepancies between HESS and
    … …  
    110110\cite{Aharonian2005,Atoyan2004,Horns2004}. The GC is rich in massive stellar
    111111clusters with up to 100 OB stars \cite{GC_environment}, immersed in a dense
    112 gas within a radius of 300 pc and the mass of $2.7 \cdot 10^7 M_{\odot}$,
    113 young supernova remnants e.g. G0.570-0.018 or Sgr A East, and nonthermal radio arcs. The dynamical center of the Milky Way is associated with the compact radio source Sgr A$^*$, which is believed to be a massive black hole \cite{GC_black_hole,Melia2001}. An overview of the sources in the GC region is given in Figure \ref{fig:GC_sources}. Some data about the GC are summarized in Table \ref{table:GC_properties}.
     112gas. There are young supernova remnants e.g. G0.570-0.018 or Sgr A East, and nonthermal radio arcs. The dynamical center of the Milky Way is associated with the compact radio source Sgr A$^*$, which is believed to be a massive black hole \cite{GC_black_hole,Melia2001}. Within a radius of 300 pc around the Galactic Center there is a mass of $2.7 \cdot 10^7 M_{\odot}$. An overview of the sources in the GC region is given in Figure \ref{fig:GC_sources}. Some data about the GC are summarized in Table \ref{table:GC_properties}.
    114113
    115114
    … …  
    141140extending up to at least 10 GeV, with a spectral index of 1.3 below the break at a few
    142141GeV. Assuming a distance of 8.5 kpc, the gamma ray luminosity of this source
    143 is very large $~2.2 \cdot 10^{37} \mathrm{erg}/\mathrm{s}$, which is
     142is very large, $~2.2 \cdot 10^{37} \mathrm{erg}/\mathrm{s}$, which is
    144143equivalent to about 10 times the gamma flux from the Crab nebula. An independent analysis of the EGRET data
    145144\cite{Hooper2002} indicates a point source whose position is different from the GC at a confidence level beyond 99.9 \%. %\cite{Hooper2002, A&A 335 (1998) 161}
    … …  
    156155\includegraphics[totalheight=6cm]{sgr_figure4.eps}
    157156\end{center}
    158 \caption[Gamma flux from GC.]{The VHE gamma flux as observed by Whipple, Cangaroo , HESS and by the EGRET experiment \cite{GC_hess}.} \label{fig:GC_gamma_flux}
     157\caption[Gamma flux from GC.]{The VHE gamma flux from the Galactic Center as observed by Whipple, Cangaroo , HESS and by the EGRET experiment \cite{GC_hess}.} \label{fig:GC_gamma_flux}
    159158\end{figure}
    160159
    … …  
    164163\includegraphics[totalheight=8cm]{gc_legend.eps}
    165164\end{center}
    166 \caption[Gamma flux from GC.]{The source locations as measured by the other IACTs \cite{Horns2004}.} \label{fig:GC_source_location}
    167 \end{figure}
    168 
    169 The discrepancies between the measured flux spectra could indicate inter-calibration problems between the IACTs. An apparent source variability of the order of one year could be due to the different regions in which the signal is integrated.
     165\caption[Gamma flux from GC.]{The source locations as measured by the other IACTs Whipple, Cangaroo and HESS \cite{Horns2004}.} \label{fig:GC_source_location}
     166\end{figure}
     167
     168The discrepancies between the measured flux spectra could indicate inter-calibration problems between the IACTs. It could indicate an apparent source variability of the order of one year or it could be due to the different regions in which the signal is integrated.
     169
     170%An apparent source variability of the order of one year could be due to the different regions in which the signal is integrated.
    170171
    171172
    … …  
    197198\end{table}
    198199
    199 The principal investigator is .......
     200S. Commichau and H. Bartko are nominated to be principle investigators in order to allow for a continous contact person till the final publication of the results.
     201
     202%The principal investigator is shared between S. Commichau and H. Bartko to allow for
     203
    200204
    201205\section{Scientific Case}
    … …  
    239243\subsection{Models for the gamma-ray emission from Sgr A$^*$}
    240244
    241 Production of high-energy gamma rays within 10 Schwarzschild radii of a black hole (of any mass) could be copious because of effective acceleration of particles by the rotation-induced electric fields close to the event horizon or by strong shocks in the inner parts of the accretion disk. However, these energetic gamma rays generally cannot escape the source because of severe absorption due to interactions with the dense, low-frequency radiation through photon-photon pair production. Fortunately the supermassive black hole in our Galaxy is an exception because of its unusually low bolometric luminosity. The propagation effects related to the possible cascading in the photon filed may extend the high-energy limit to 10 TeV or even beyond \cite{Aharonian2005}.
     245Production of high-energy gamma rays within 10 Schwarzschild radii of a black hole (of any mass) could be copious because of effective acceleration of particles by the rotation-induced electric fields close to the event horizon or by strong shocks in the inner parts of the accretion disk. However, these energetic gamma rays generally cannot escape the source because of severe absorption due to interactions with the dense, low-frequency radiation through photon-photon pair production. Fortunately the supermassive black hole in our Galaxy is an exception because of its unusually low bolometric luminosity. The propagation effects related to the possible cascading in the photon field may extend the high-energy limit to 10 TeV or even beyond \cite{Aharonian2005}.
    242246
    243247
    … …  
    245249\subsubsection{Leptonic Models}
    246250
    247 Also advection dominated accretion flow (ADAF) models can describe the production of high-energy gamma radiation in the Galactic Center \cite{Atoyan2004}.
     251Many proposed acceleration mechanisms of VHE gamma radiation in the Galactic Center are based on so called advection dominated accretion flow (ADAF) models \cite{Atoyan2004}.
     252
     253%Also advection dominated accretion flow (ADAF) models can describe the production of high-energy gamma radiation in the Galactic Center \cite{Atoyan2004}.
    248254
    249255A viable site of acceleration of highly energetic electrons could be the compact region within a few gravitational radii of the black hole. In this case the electrons produce not only curvature radiation, which peaks around 1 GeV, but also inverse Compton gamma rays (produced in the Klein-Nishina regime) with the peak emission around 100 TeV. As these high-energy gammas cannot escape the source the observed gamma rays would be due to an electromagnetic cascade.
    … …  
    253259One scenario is related to protons accelerated to about $10^{18}$ eV \cite{Aharonian2005}. These protons produce gamma rays via photo-meson processes. This scenario also predicts detectable fluxes of  $10^{18}$ eV neutrons and perhaps gamma rays and neutrinos. A hint of an excess of highest energy neutrons from the GC has been reported in \cite{Hayashida1999}.
    254260
    255 TeV gamma rays can also be produced by significantly  lower energy protons, accelerated by the electric filed close to the gravitational radius or by strong shocks in the accretion disk. In this case the gamma-ray production is dominated by interactions of $10^{13}$ eV protons with the accretion plasma. This scenario predicts a neutrino flux which should be observable with northern neutrino telescopes like NEMO. It also predicts strong TeV--X-ray--IR correlations.
     261TeV gamma rays can also be produced by significantly  lower energy protons, accelerated by the electric filed close to the gravitational radius of the black hole or by strong shocks in the accretion disk \cite{Aharonian2005}. In this case the gamma-ray production is dominated by interactions of $10^{13}$ eV protons with the accretion plasma. This scenario predicts a neutrino flux which should be observable with northern neutrino telescopes like NEMO and Antares. It also predicts strong TeV--X-ray--IR correlations.
    256262
    257263
    … …  
    261267The presence of a Dark Matter halo of the Galaxy is well established by stellar dynamics \cite{Klypin2002}. At present, the nature of Dark Matter is unknown, but a number of viable candidates have been advocated within different theoretical frameworks, mainly motivated by particle physics (for a review see \cite{jung96}) including the widely studied models of supersymmetric (SUSY) Dark Matter \cite{Ellis1984}. Also models involving extra dimensions are discussed like Kaluza-Klein Dark Matter \cite{Kaluza_Klein,Bergstrom2004}.
    262268
    263 The supersymmetric particle dark matter candidates might self-annihilate into boson or fermion pairs yielding very high-energy gammas in subsequent decays and from hadronisation. The gamma flux above an energy threshold $E_{\mathrm{thresh}}$ per solid angle $\Omega$ is given by:
     269The supersymmetric particle dark matter candidates might self-annihilate into boson or fermion pairs yielding very high-energy gammas in subsequent decays and from hadronisation. The gamma flux above an energy threshold $E_{\mathrm{th}}$ per solid angle $\Omega$ is given by:
    264270
    265271\begin{equation*}
    266 \frac{\text{d} N_{\gamma}(E_{\gamma}>E_{\mathrm{thresh}})}{\text{d}t\  \text{d}A\  \text{d}\Omega }= N_{\gamma}(E_{\gamma}>E_{\mathrm{thresh}}) \cdot \frac{1}{2} \cdot \frac{\langle \sigma v \rangle}{4 \pi m_{\chi}^2} \cdot  \int_{\text{los}}\rho_{\chi}^2(\vec{r}(s,\Omega)) \text{d}s \ ,
     272\frac{\text{d} N_{\gamma}(E_{\gamma}>E_{\mathrm{th}})}{\text{d}t\  \text{d}A\  \text{d}\Omega }= N_{\gamma}(E_{\gamma}>E_{\mathrm{th}}) \cdot \frac{1}{2} \cdot \frac{\langle \sigma v \rangle}{4 \pi m_{\chi}^2} \cdot  \int_{\text{los}}\rho_{\chi}^2(\vec{r}(s,\Omega)) \text{d}s \ ,
    267273\end{equation*}
    268274
    269275
    270 where $\langle \sigma v \rangle$ is the thermally averaged annihilation cross section, $m_{\chi}$ the mass and $\rho_{\chi}$ the spatial density distribution of the hypothetical dark matter particles. $N_{\gamma}(E_{\gamma}>E_{\mathrm{thresh}})$ is the gamma yield above the threshold energy per annihilation. The predicted flux depends on the SUSY parameters and on the spatial distribution of the dark matter. The energy spectrum of the produced gamma radiation has a very characteristic feature : a sharp cut-off at the mass of the dark matter particle. Also the flux should be absolutely stable in time.
     276where $\langle \sigma v \rangle$ is the thermally averaged annihilation cross section, $m_{\chi}$ the mass and $\rho_{\chi}$ the spatial density distribution of the hypothetical dark matter particles. $N_{\gamma}(E_{\gamma}>E_{\mathrm{th}})$ is the gamma yield above the threshold energy per annihilation. The predicted flux depends on the SUSY parameters and on the spatial distribution of the dark matter. The energy spectrum of the produced gamma radiation has a very characteristic feature : a sharp cut-off at the mass of the dark matter particle. Also the flux should be absolutely stable in time.
    271277
    272278Numerical simulations of cold dark matter \cite{NFW1997,Stoehr2002,Hayashi2004,Moore1998} predict universal DM halo profiles with a density enhancement in the center of the dark halos. In the very center the dark matter density can be even more enhanced through an adiabatic compression due to the baryons \cite{Prada2004} present. All dark matter distributions that predict observable fluxes are cusped, yielding an approximately point-like source.
    … …  
    279285
    280286Figure \ref{fig:exclusion_lmits} shows exclusion limits for MAGIC (solid straight lines) for the four most promising sources,
    281 in the plane $N_{\gamma}(E_{\gamma}>E_{\mathrm{thresh}})\langle \sigma v \rangle$ vs. $m_{\chi}$. The energy threshold $E_{th}$ has been assumed to be 100 GeV. Due to its proximity the GC yields the largest expected flux from particle dark matter annihilation and thus the lowest exclusion limit. Nevertheless, this minimum measurable flux is more than one order of magnitude above the highest fluxes predicted by SUSY models (full circles). Also the flux measured by the HESS experiment is far above the theoretical expectation (dotted line).
     287in the plane $N_{\gamma}(E_{\gamma}>E_{\mathrm{th}})\langle \sigma v \rangle$ vs. $m_{\chi}$. The energy threshold $E_{\mathrm{th}}$ has been assumed to be 100 GeV. Due to its proximity the GC yields the largest expected flux from particle dark matter annihilation and thus the lowest exclusion limit. Nevertheless, this minimum measurable flux is more than one order of magnitude above the highest fluxes predicted by SUSY models (full circles). Also the flux measured by the HESS experiment is far above the theoretical expectation (dotted line).
    282288
    283289
    … …  
    379385\begin{tabular}{c|cccc}
    380386 \hline
    381  ZA          &  $E_{th}$      & sensitivity    & $\Phi(E>E_{th})$           
     387 ZA          &  $E_{\mathrm{th}}$      & sensitivity    & $\Phi(E>E_{\mathrm{th}})$           
    382388                              & $T_{5\sigma}$       \\
    383              &                & above $E_{th}$ &   &\\
     389             &                & above $E_{\mathrm{th}}$ &   &\\
    384390$[^{\circ}]$ & $[{\rm GeV}]$  & $[{\rm cm}^2\;{\rm s}]^{-1}$ 
    385391                              & $[{\rm cm}^2\;{\rm s}]^{-1}$     
    … …  
    390396\hline
    391397\end{tabular}
    392 \caption{Energy threshold $E_{th}$ and sensitivity for MAGIC for 2 zenith angles ZA. The 4th and 5th column contain the expected integrated flux above $E_{th}$ and the time needed for observing a 5$\sigma$ excess, respectively.}\label{table:MAGIC_sensitivity}}
     398\caption{Energy threshold $E_{\mathrm{th}}$ and sensitivity for MAGIC for 2 zenith angles ZA. The 4th and 5th column contain the expected integrated flux above $E_{\mathrm{th}}$ and the time needed for observing a 5$\sigma$ excess, respectively.}\label{table:MAGIC_sensitivity}}
    393399\end{table}
    394400
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