Changeset 6834
- Timestamp:
- 03/16/05 15:11:15 (20 years ago)
- File:
-
- 1 edited
-
trunk/MagicSoft/GC-Proposal/GC.tex (modified) (13 diffs)
Legend:
- Unmodified
- Added
- Removed
-
trunk/MagicSoft/GC-Proposal/GC.tex
r6833 r6834 73 73 \begin{itemize} 74 74 \item to measure the gamma-ray flux and its energy dependence (due to the high 75 zenith angles higher energies are accessible),75 zenith angles higher energies up to about 20 TeV are accessible), 76 76 \item to inter-calibrate MAGIC and HESS, 77 77 \item to help resolving the flux discrepancies between HESS and … … 110 110 \cite{Aharonian2005,Atoyan2004,Horns2004}. The GC is rich in massive stellar 111 111 clusters 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}. 112 gas. 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}. 114 113 115 114 … … 141 140 extending up to at least 10 GeV, with a spectral index of 1.3 below the break at a few 142 141 GeV. 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 is142 is very large, $~2.2 \cdot 10^{37} \mathrm{erg}/\mathrm{s}$, which is 144 143 equivalent to about 10 times the gamma flux from the Crab nebula. An independent analysis of the EGRET data 145 144 \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} … … 156 155 \includegraphics[totalheight=6cm]{sgr_figure4.eps} 157 156 \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} 159 158 \end{figure} 160 159 … … 164 163 \includegraphics[totalheight=8cm]{gc_legend.eps} 165 164 \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} 167 168 The 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. 170 171 171 172 … … 197 198 \end{table} 198 199 199 The principal investigator is ....... 200 S. 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 203 200 204 201 205 \section{Scientific Case} … … 239 243 \subsection{Models for the gamma-ray emission from Sgr A$^*$} 240 244 241 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 fi led may extend the high-energy limit to 10 TeV or even beyond \cite{Aharonian2005}.245 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 field may extend the high-energy limit to 10 TeV or even beyond \cite{Aharonian2005}. 242 246 243 247 … … 245 249 \subsubsection{Leptonic Models} 246 250 247 Also advection dominated accretion flow (ADAF) models can describe the production of high-energy gamma radiation in the Galactic Center \cite{Atoyan2004}. 251 Many 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}. 248 254 249 255 A 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. … … 253 259 One 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}. 254 260 255 TeV gamma rays can also be produced by significantly lower energy protons, accelerated by the electric filed close to the gravitational radius o r 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.261 TeV 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. 256 262 257 263 … … 261 267 The 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}. 262 268 263 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 $E_{\mathrm{th resh}}$ per solid angle $\Omega$ is given by:269 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 $E_{\mathrm{th}}$ per solid angle $\Omega$ is given by: 264 270 265 271 \begin{equation*} 266 \frac{\text{d} N_{\gamma}(E_{\gamma}>E_{\mathrm{th resh}})}{\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 \ , 267 273 \end{equation*} 268 274 269 275 270 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. $N_{\gamma}(E_{\gamma}>E_{\mathrm{th resh}})$ 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.276 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. $N_{\gamma}(E_{\gamma}>E_{\mathrm{th}})$ 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. 271 277 272 278 Numerical 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. … … 279 285 280 286 Figure \ref{fig:exclusion_lmits} shows exclusion limits for MAGIC (solid straight lines) for the four most promising sources, 281 in the plane $N_{\gamma}(E_{\gamma}>E_{\mathrm{th resh}})\langle \sigma v \rangle$ 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).287 in 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). 282 288 283 289 … … 379 385 \begin{tabular}{c|cccc} 380 386 \hline 381 ZA & $E_{ th}$ & sensitivity & $\Phi(E>E_{th})$387 ZA & $E_{\mathrm{th}}$ & sensitivity & $\Phi(E>E_{\mathrm{th}})$ 382 388 & $T_{5\sigma}$ \\ 383 & & above $E_{ th}$ & &\\389 & & above $E_{\mathrm{th}}$ & &\\ 384 390 $[^{\circ}]$ & $[{\rm GeV}]$ & $[{\rm cm}^2\;{\rm s}]^{-1}$ 385 391 & $[{\rm cm}^2\;{\rm s}]^{-1}$ … … 390 396 \hline 391 397 \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}} 393 399 \end{table} 394 400
Note:
See TracChangeset
for help on using the changeset viewer.
