Changeset 6220 for trunk/MagicSoft
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- 02/03/05 09:18:27 (20 years ago)
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trunk/MagicSoft/GRB-Proposal/Introduction.tex
r6219 r6220 23 23 as well as photon-pion production~\cite{WAXMAN,BAHCALL,BOETTCHER} and inverse-Compton scattering 24 24 in 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}.\\ 25 Long-term HE $\gamma$-emission from accelerated protons in the forward-shock has been predicted in~\cite{LI}. 26 This model predicts GeV inverse Compton emission even one day after the burst. 27 Even considering pure electron-synchrotron radiation, measurable GeV-emission for a significant 28 fraction of GRBs is predicted~\cite{ZHANG2}.\\ 27 29 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}. 30 GeV-emission in GRBs is particularly sensitive to the Lorentz factor and the photon density of the 31 emitting material -- 32 and 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. 34 Direct comparison of the prompt GRB flux at $\sim$\,10\,GeV and $\sim$\,100\,keV may 35 allow to determine the magnetic field strength~\cite{ASAF2}. 31 36 32 37 \par … … 34 39 Several attempts have been made in the past to observe GRBs in the GeV range, 35 40 each 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) 41 The only significant detection was performed by \eg which was able to observe seven GRBs 42 emitting high energy (HE) 37 43 photons 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}. 38 44 There have been results suggesting gamma rays beyond the GeV range from the TIBET air shower array 39 45 in 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).\\ 46 Whipple Air Cherenkov Telescope~\cite{CONNAUGHTON1}, and coincident and monitoring studies by 47 HEGRA-AIROBICC~\cite{PADILLA}, Whipple~\cite{CONNAUGHTON2} and the Milagro prototype Milagrito~\cite{MILAGRO}. 48 The GRAND array has reported some excess of observed muons during seven BATSE bursts~\cite{GRAND}. 49 In this context, especially the publication from the TASC detector on \eg is important~\cite{GONZALES}, 50 finding a HE spectral component presumably due to the ultra-relativistic acceleration of hadrons and 51 producing a spectral index of $-1$ with no cut-off up to the detector energy limit at 200\,MeV.\\ 41 52 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). 53 Concerning estimates of the \ma GRB observability, a study of GRB spectra obtained from the 54 third and fourth \ba catalogue has been made in~\cite{ICRC,NICOLA}. The spectra were extrapolated to GeV 55 energies with a simple continuation of the observed high-energy power law behaviour and the calculated 56 fluxes compared with \ma sensitivities. Setting conservative cuts on observation times and significances, 57 and assuming an energy threshold of 15~GeV, a 5\,$\sigma$-signal rate of $0.5-2$ per year 58 was 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 60 those observed by \ma, this number will still have to be lowered. 46 61 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. 62 Taking into account the local rate of GRBs estimated in~\cite{GUETTA}, late afterglow emission from a 63 few tens of GRBs per year should be observable over the whole sky above our energy threshold. 64 The model of~\cite{ASAF2} predict delayed GeV-emission that should be significantly detectable by \ma 65 in 100\,sec. 49 66 50 67 \subsection{Observation of XRFs} 51 68 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. 69 While the major energy from the prompt GRBs is emitted in $\gamma$-rays with a peak energy of 200\,keV, 70 X-ray flashes (XRFs) are characterized 71 by peak energies below 50~keV and a dominant X-ray fluence. Because of similar properties, a connection 72 between XRFs and GRBs is suggested. 73 The most popular theories suggest that XRFs are produced from GRBs observed ''off-axis''. 74 Alternatively, an increase of the baryon load within the fireball itself or low efficiency shocks could 75 produce XRFs. 56 76 If there is a connection between the XRFs and GRBs, they should originate at rather low redshifts (z $<$ 0.6).\\ 57 77 58 Gamma-ray satellites react in the same way to XRFs and GRBs. In case of a detection the coordinates are distributed 78 Gamma-ray satellites react in the same way to XRFs and GRBs. 79 In case of a detection the coordinates are distributed 59 80 to other observatories (see section 2.1). Only from later analysis the difference can be established. 60 81 61 82 \par 62 83 63 In this case we include also the observation of XRFs by MAGIC in ourproposal.84 We include therefore the observation of XRFs by \ma in this proposal. 64 85 65 86 \subsection{Observation of SGRs} 66 87 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.\\ 88 Soft Gamma Repeaters (SGRs) are believed to be extremely rare strong magnetic neutron stars that 89 periodically emit $\gamma$-rays. Only four identified SGRs were discovered in the last 20 years: 90 SGR0526-66, SGR1806-20, SGR1900+14, SGR1627-41. 91 GRBs and SGRs can be explained within one same gamma jet model where the jet is observed at different 92 beam-angles and at different ages.\\ 68 93 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. 94 The BAT instrument on the SWIFT satellite triggered on an outburst from SGR1806-20 on 30. January 2005. 95 The fluence was about $10^{-5}$\,erg/cm$^2$ in the range between 15 and 350\,keV. 96 This event was five orders of magnitude smaller than the giant flare from this source on the 97 December 27$^{th}$, 2004. 98 If a giant flare from SGR occurs as SGR1806-20, MAGIC would be able to detect the $\gamma$-ray 99 emission from the source with 100\,sec. observationes time. 70 100 71 101
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