Changeset 6105
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- 01/28/05 18:58:51 (20 years ago)
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trunk/MagicSoft/GRB-Proposal/Strategies.tex
r6101 r6105 76 76 We determine the maximum zenith angle by requiring that the overwhelming majority of 77 77 possible GRBs will yield an in principle observable spectrum. Figure~\ref{fig:grh} 78 shows the gamma-ray horizon (GRH) as computed in~\cite{KNEISKE}. The GRH is defined as the 79 gamma-ray energy at which a part of $1/e$ of a hypothiszed mono-energetic flux is absorbed after 80 travelling a distance of $d$, expressed in redshift $z$ from the earth. One can see that at typical 81 GRB distances of $z=1$, all gamma-rays above 100\,GeV get absorbed before they reach the earth. 82 \par 83 Even the closest GRB with known redshift ever observed, GRB030329~\cite{GRB030329}, lies at a redshift 84 of $z=0.1685$. In this case, gamma-rays above 200\,GeV get absorbed. 78 85 79 80 \begin{figure} 86 \begin{figure}[htp] 81 87 \centering 82 \includegraphics[width=0. 99\linewidth]{f4.eps}83 \caption{ }88 \includegraphics[width=0.85\linewidth]{f4.eps} 89 \caption{Gamma Ray Horizon, as derived in~\cite{KNEISKE}} 84 90 \label{fig:grh} 85 91 \end{figure} 92 93 \par 94 We assume now an energy threshold of 50\,GeV for MAGIC at a zenith angle of $\theta = 0$. According 95 to~\cite{eckart}, the energy threshold of a Cherenkov telescope scales with zenith angle like: 96 97 \begin{equation} 98 E^{thr}(\theta) = E^{thr}(0) \cdot \cos(\theta)^{-2.7} 99 \label{eq:ethrvszenith} 100 \end{equation} 101 102 Eq.~\ref{eq:ethrvszenith} leads to an energy threshold of about 900\,GeV at $\theta = 70^\circ$ and 103 500\,GeV at $\theta = 65^\circ$. Inserting these results into the GRH (figure~\ref{fig:grh}), one gets 104 a maximal observable GRB distance of $z = 0.1$ and $z = 0.2$, respectively. We think that the probability for 105 GRBs to occur at these distances is suffiently small in order to neglect the very difficult observations 106 beyond these limits. 86 107 87 108 \subsection{In case of follow-up: Next steps}
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