Changeset 6220 for trunk/MagicSoft


Ignore:
Timestamp:
02/03/05 09:18:27 (20 years ago)
Author:
gaug
Message:
*** empty log message ***
File:
1 edited

Legend:

Unmodified
Added
Removed
  • trunk/MagicSoft/GRB-Proposal/Introduction.tex

    r6219 r6220  
    2323as well as photon-pion production~\cite{WAXMAN,BAHCALL,BOETTCHER} and inverse-Compton scattering
    2424in the burst environment~\cite{MESZAROS93,CHIANG,PILLA,ZHANG2,BELOBORODOV}.
    25 Long-term HE $\gamma$ emission from accelerated protons in the forward-shock has been predicted in~\cite{LI}. This model predicts GeV inverse Compton emission even one day after the burst.
    26 Even considering pure electron-synchrotron radiation, measurable GeV emission for a significant fraction of GRBs is predicted~\cite{ZHANG2}.\\
     25Long-term HE $\gamma$-emission from accelerated protons in the forward-shock has been predicted in~\cite{LI}.
     26This model predicts GeV inverse Compton emission even one day after the burst.
     27Even considering pure electron-synchrotron radiation, measurable GeV-emission for a significant
     28fraction of GRBs is predicted~\cite{ZHANG2}.\\
    2729
    28 GeV emission in GRBs is particularly sensitive to the Lorentz factor and the photon density of the emitting material -
    29 and thus to the distance of the radiating shock from the source - due to the \linebreak
    30 $\gamma~\gamma \rightarrow$ \textit{e$^+$~e$^-$} absorption in the emission region. Direct comparison of the prompt GRB flux at $\sim$ 10\,GeV and $\sim$ 100\,keV may allow to determine the magnetic field strength~\cite{ASAF2}.
     30GeV-emission in GRBs is particularly sensitive to the Lorentz factor and the photon density of the
     31emitting material --
     32and thus to the distance of the radiating shock from the source -- due to the
     33$\gamma \gamma \rightarrow \textrm{e}^+\textrm{e}^-$ absorption in the emission region.
     34Direct comparison of the prompt GRB flux at $\sim$\,10\,GeV and $\sim$\,100\,keV may
     35allow to determine the magnetic field strength~\cite{ASAF2}.
    3136
    3237\par
     
    3439Several attempts have been made in the past to observe GRBs in the GeV range,
    3540each indicating some excess over background but without stringent evidence.
    36 The only significant detection was performed by \eg which detected seven GRBs emitting high energy (HE)
     41The only significant detection was performed by \eg which was able to observe seven GRBs
     42emitting high energy (HE)
    3743photons in the 100\,MeV to 18\,GeV range~\cite{EGRET, DINGUS1}. The data shows no evidence of a HE cut-off in the GRB spectrum~\cite{DINGUS2}. Recent results indicate that the spectrum of some GRBs contains a very hard, luminous, long-duration component~\cite{GONZALES}.
    3844There have been results suggesting gamma rays beyond the GeV range from the TIBET air shower array
    3945in coincidence with BATSE bursts~\cite{AMENOMORI}, rapid follow-up observations by the
    40 Whipple Air Cherenkov Telescope~\cite{CONNAUGHTON1}, and coincident and monitoring studies by HEGRA-AIROBICC~\cite{PADILLA}, Whipple~\cite{CONNAUGHTON2} and the Milagro prototype Milagrito~\cite{MILAGRO}. The GRAND array has reported some excess of observed muons during seven BATSE bursts~\cite{GRAND}. In this context, especially the publication from the TASC detector on \eg is important~\cite{GONZALES}, finding a HE 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 energy limit (200\,MeV).\\
     46Whipple Air Cherenkov Telescope~\cite{CONNAUGHTON1}, and coincident and monitoring studies by
     47HEGRA-AIROBICC~\cite{PADILLA}, Whipple~\cite{CONNAUGHTON2} and the Milagro prototype Milagrito~\cite{MILAGRO}.
     48The GRAND array has reported some excess of observed muons during seven BATSE bursts~\cite{GRAND}.
     49In this context, especially the publication from the TASC detector on \eg is important~\cite{GONZALES},
     50finding a HE spectral component presumably due to the ultra-relativistic acceleration of hadrons and
     51producing a spectral index of $-1$ with no cut-off up to the detector energy limit at 200\,MeV.\\
    4152
    42 Concerning estimates of \ma GRB observability, a very detailed study of GRB spectra obtained from the
    43 third and fourth \ba catalogue has been made in~\cite{ICRC,NICOLA}. The spectra were extrapolated to GeV 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,
    44 and assuming an energy threshold of 15~GeV, a GRB detection rate of $0.5-2$ per year
    45 was obtained for an assumed observation delay between 15 and 60 sec. and a \ba trigger rate ($\sim$\,360/year).
     53Concerning estimates of the \ma GRB observability, a study of GRB spectra obtained from the
     54third and fourth \ba catalogue has been made in~\cite{ICRC,NICOLA}. The spectra were extrapolated to GeV
     55energies with a simple continuation of the observed high-energy power law behaviour and the calculated
     56fluxes compared with \ma sensitivities. Setting conservative cuts on observation times and significances,
     57and assuming an energy threshold of 15~GeV, a 5\,$\sigma$-signal rate of $0.5-2$ per year
     58was obtained for an assumed observation delay between 15 and 60\,sec. and a \ba trigger rate
     59($\sim$\,360/year). As the \sw alert rate is about a factor~2 lower including even fainter bursts than
     60those observed by \ma, this number will still have to be lowered.
    4661
    47 Taking into account the local rate of GRBs estimated in~\cite{GUETTA}, late afterglow emission from few tens of GRBs per year
    48 should be observable above our energy threshold. The model of~\cite{ASAF2} predict delayed GeV emission that should be significantly detectable by MAGIC in 100\,seconds.
     62Taking into account the local rate of GRBs estimated in~\cite{GUETTA}, late afterglow emission from a
     63few tens of GRBs per year should be observable over the whole sky above our energy threshold.
     64The model of~\cite{ASAF2} predict delayed GeV-emission that should be significantly detectable by \ma
     65in 100\,sec.
    4966
    5067\subsection{Observation of XRFs}
    5168
    52 While the major energy from the prompt GRBs is emitted in $\gamma$-rays ($E_p \sim$ 200~keV), XRFs are characterized
    53 by peak energies below 50~keV and a dominant X-ray fluence. Because of similar properties a connection between XRFs and GRBs is
    54 suggested. The most popular theories say that XRFs are produced from GRBs observed ''off-axis''.
    55 Alternatively, an increase of the baryon load within the fireball itself or low efficiency shocks can produce XRFs.
     69While the major energy from the prompt GRBs is emitted in $\gamma$-rays with a peak energy of 200\,keV,
     70X-ray flashes (XRFs) are characterized
     71by peak energies below 50~keV and a dominant X-ray fluence. Because of similar properties, a connection
     72between XRFs and GRBs is suggested.
     73The most popular theories suggest that XRFs are produced from GRBs observed ''off-axis''.
     74Alternatively, an increase of the baryon load within the fireball itself or low efficiency shocks could
     75produce XRFs.
    5676If there is a connection between the XRFs and GRBs, they should originate at rather low redshifts (z $<$ 0.6).\\
    5777
    58 Gamma-ray satellites react in the same way to XRFs and GRBs. In case of a detection the coordinates are distributed
     78Gamma-ray satellites react in the same way to XRFs and GRBs.
     79In case of a detection the coordinates are distributed
    5980to other observatories (see section 2.1). Only from later analysis the difference can be established.
    6081
    6182\par
    6283
    63 In this case we include also the observation of XRFs by MAGIC in our proposal.
     84We include therefore the observation of XRFs by \ma in this proposal.
    6485
    6586\subsection{Observation of SGRs}
    6687
    67 Soft Gamma Repeaters (SGRs) are extremely rare strong magnetic neutron stars that periodically emit $\gamma$-rays. Only four identified SGRs were discovered in the last 20 years: SGR0526-66, SGR1806-20, SGR1900+14, SGR1627-41. GRBs and SGRs can be explained with an unique processing gamma jet model observed at different beam-angle and at different ages.\\
     88Soft Gamma Repeaters (SGRs) are believed to be extremely rare strong magnetic neutron stars that
     89periodically emit $\gamma$-rays. Only four identified SGRs were discovered in the last 20 years:
     90SGR0526-66, SGR1806-20, SGR1900+14, SGR1627-41.
     91GRBs and SGRs can be explained within one same gamma jet model where the jet is observed at different
     92beam-angles and at different ages.\\
    6893
    69 The BAT instrument on the SWIFT satellite triggered on an outburst from SGR1806-20 on 30. January 2005. The fluence was $\sim$ 1$\times$10$^{-5}$erg/cm$^2$(15-350keV). This event was five orders of magnitude smaller than the giant flare from this source on the 27. December 2004. If a giant flare from SGR occurs as SGR1806-20, MAGIC would be able to detect the $\gamma$-ray emission from the source with 100 seconds observationes time.
     94The BAT instrument on the SWIFT satellite triggered on an outburst from SGR1806-20 on 30. January 2005.
     95The fluence was about $10^{-5}$\,erg/cm$^2$ in the range between 15 and 350\,keV.
     96This event was five orders of magnitude smaller than the giant flare from this source on the
     97December 27$^{th}$, 2004.
     98If a giant flare from SGR occurs as SGR1806-20, MAGIC would be able to detect the $\gamma$-ray
     99emission from the source with 100\,sec. observationes time.
    70100
    71101
Note: See TracChangeset for help on using the changeset viewer.