source: trunk/MagicSoft/GRB-Proposal/Introduction.tex@ 5988

\section{Introduction}
The MAGIC telescope has been designed especially light with a special focus on 
being able to react fastly to GRB alerts from the satellites. 
In \cite{design} and~\cite{PETRY}, 
the objective was set to turn the telescope to the burst position in 10-30~s 
in order to have a fair chance of detecting a burst with the MAGIC telescope. 
The current possible value is 20 sec. for full turn-around 
%FIXME
{\it \bf THIS HAS TO BE CHECKED FROM THOMAS B. !!}
\par
Several attempts have been made in the past to observe GRBs at energies 
from the GeV range upwards each indicating some excess over background but 
without stringent evidence. The only secured detection was performed by EGRET 
which detected seven GRBs emitting high energy photons in the 
100~MeV to 18~GeV range~\cite{EGRET}. There have been 
results suggesting gamma rays beyond the GeV range from the TIBET array~\cite{TIBET} and 
from HEGRA-AIROBICC~\cite{HEGRA}. Evidence for TeV emission of one burst was claimed by 
the MILAGRITO experiment~\cite{MILAGRO}. Recently, the GRAND array has reported some 
excess of observed muons during seven BATSE bursts~\cite{GRAND}. In this context, note 
especially a recent publication from the TASC detector on \eg~\cite{TASC}, 
finding a high-energy spectral 
component presumably due to ultra-relativistic acceleration of hadrons and 
producing a spectral index of $-1$ with no cut-off up to the detector limit (200 MeV). 
\par
The nowadays most widely accepted model for gamma emission from GRB suggests a bursts 
environment involving collisions of an ultra-relativistic e$^+$-e$^-$ 
plasma fireball~\cite{PAZCYNSKI,GOODMAN,SARI}. These fireballs may produce 
low-energy gamma rays either by ``internal'' collisions of multiple 
shocks~\cite{XU,REES} or by ``external'' collisions of a single shock 
with the ambient circum burst medium (CBM)~\cite{MESZAROS94}. 
\par
In many publications, 
the possibility that more energetic gamma-rays come along with the (low-energy) gamma-ray 
burst, have been explored.
Proton-synchrotron emission~\cite{TOTANI} have 
been suggested as well as photo-pion production~\cite{WAXMAN,BAHCALL,BOETTCHER} 
and inverse-Comption 
scattering in the burst environment~\cite{MESZAROS93,CHIANG,PILLA,ZHANG}.
Long-term high-energy gamma emission from accelerated protons in forward-shock 
has been predicted in~\cite{LI}.
Even considering pure electron-synchrotron radiation predicts measurable GeV emission for a 
significant fraction of GRBs~\cite{ZHANG}.
Implications of the observation of a high-energy gamma-ray component on 
distance scale, energy production in the GRB and distinction between internal and 
external shock models have been treated in~\cite{HARTMANN,MANNHEIM,SALOMON,PRIMACK}.
\par
\ldots {\bf MORE ELABORATE TREATMENT OF HE-EMISSION: WHICH MODELS, WHAT TIME DIFFERENCE TO 
GRB, TIME DEVELOPMENT, EXPECTED FLUXES, SPECTRA } \ldots
\par
In the year 2005, three satellites will produce GRB alerts: The \he 
satellite, launched in October 2000, the \ig satellite, launched October 2002 and the 
\sw satellite, launched in October, 2004 and expected to be fully operational in March, 2005.
\par
Concerning estimates about the MAGIC observability of GRBs, a very detailed study
of GRB spectra obtained from the third and fourth \ba catalogue has been made 
in~\cite{ICRC,NICOLA}. The spectra were extrapolated to \ma energies with a simple continuation 
of the observed high-energy power law behaviour and the calculated fluxes compared 
with \ma sensitivities. Setting conservative cuts on observation times and significances, 
and assuming an energy threshold of 15~GeV, a GRB detection rate of $0.5--2$ per year
was obtained for an assumed observation delay of 15~sec. and the \sw GRB trigger rate ($\sim 100/year$).