Changeset 6255
- Timestamp:
- 02/04/05 14:36:37 (20 years ago)
- Location:
- trunk/MagicSoft/GRB-Proposal
- Files:
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- 2 edited
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Introduction.tex (modified) (2 diffs)
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Strategies.tex (modified) (7 diffs)
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trunk/MagicSoft/GRB-Proposal/Introduction.tex
r6251 r6255 69 69 While the major energy from the prompt GRBs is emitted in $\gamma$-rays with a peak energy of 200\,keV, 70 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 ~\cite{DADO} suggest that XRFs are produced from GRBs observed ''off-axis''. 74 Alternatively, an increase of the baryon load within the fireball itself ~\cite{HUANG} or low efficiency shocks ~\cite{BARRAUD} could produce XRFs. 75 If there is a connection between XRFs and GRBs, they should originate at rather low redshifts (z $<$ 0.6). Because If XRFs lie at large distances, their energies would not fit the observed correlation between GRB peak energy and isotropic energy release~\cite{LEVAN}. \\ 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 Some theories~\cite{DADO} suggest that XRFs are produced from GRBs observed ''off-axis''. 74 Alternatively, an increase of the baryon load within the fireball itself~\cite{HUANG} or low efficiency 75 shocks~\cite{BARRAUD} could produce XRFs. 76 If there is a connection between XRFs and GRBs, they should originate at rather low redshifts (z $<$ 0.6) 77 because otherwise, the XRF energies would not fit into the observed correlation 78 between GRB peak energy and isotropic energy release~\cite{LEVAN}. \\ 76 79 77 80 Gamma-ray satellites react in the same way to XRFs and GRBs. … … 103 106 %%% mode: latex 104 107 %%% TeX-master: "GRB_proposal_2005" 108 %%% TeX-master: "GRB_proposal_2005" 109 %%% TeX-master: "GRB_proposal_2005" 105 110 %%% End: -
trunk/MagicSoft/GRB-Proposal/Strategies.tex
r6219 r6255 1 1 \section{Proposed Observation Strategies} 2 2 3 \subsection{Estimation of the Required Observation Time} 4 3 5 A rough estimate of the needed observation time for GRBs derives 4 from the claimed GRB observation frequency of about 150-200 GRBs/year by the \sw 5 collaboration~\cite{SWIFT} and the results of the studies on the \ma duty-cycle 6 made by Nicola Galante~\cite{NICOLA}. 7 Taking into account the calculated duty-cycle of about 10\% and a time intervall of 5 hours 8 from the onset of the GRB, we should be able to point about 1--2 GRB/month. 6 from the estimated number of GRB follow-up observations which can be 7 expressed in the following formula: 9 8 10 \par 9 \begin{equation} 10 N_{obs} = N_{alert} \cdot DC \cdot F_{overlap} 11 \end{equation} 11 12 13 where $N_{obs}$ is the mean number of observed bursts, $N_{alert}$ the mean 14 number of sent alerts, $DC$ the duty cycle (including the reduction of sky coverage 15 due to the maximum allowed zenith angle) and $F_{overlap}$ a reduction factor due to 16 the non-overlapping sky coverage between the satellites and \ma. \\ 17 18 The claimed GRB observation frequency $N_{obs}(SWIFT)$ is predicted to about 150-200 GRBs/year 19 by the \sw collaboration~\cite{SWIFT}. We estimate $DC$ from studies on the \ma duty-cycle 20 made by Nicola Galante~\cite{NICOLA}. 12 21 The duty-cycle studies are based on real weather data from the year 2002 taking the following criteria: 13 22 14 23 \begin{itemize} 15 \item maximum wind speeds of 10 m/s24 \item maximum wind speeds of 10\,m/s 16 25 \item maximum humidity of 80\% 17 26 \item darkness at astronomical horizon … … 19 28 20 29 In these duty-cycle studies also full-moon nights were considered (requiring 21 a minimum angular distance between the GRB and the moon of 30$^\circ$). 30 a minimum angular distance between the GRB and the moon of 30$^\circ$) yielding in 31 total 10\%. 22 32 23 33 \par 24 34 25 The duty-cycle in~\cite{NICOLA} will be increased by taking into account that \ma should also observe the afterglow emission of an burst that occured up to 5 hours before the start of the shift. Different GRB models predict delayed prompt GeV emission as well as acceleration of photons during the afterglows up to the threshold energy of \ma (for more details see chapter 5). 35 The duty-cycle in~\cite{NICOLA} will be increased by taking into account that \ma should also observe the 36 afterglow emission of an burst that occurred up to 5 hours before the start of the shift. 37 The afterglow observation is equivalent to an increase of the duty-cycle of about 6 days per month. 38 However, taking off the full-moon time, we remain with the anticipated 10\%.\\ 26 39 27 The afterglow observation is equivalent to an increase of the duty-cycle of about 6 days per month. 40 The overlap factor $F_{overlap}$ is difficult to estimate since the \sw satellite will continuously slew 41 to new sources or follow detected bursts. Figure~\ref{fig:orbit} shows that the satellite will pass very 42 precisely over La Palma during the night. Taking into account that it will not look towards the Sun, 43 we expect that $F_{overlap}(SWIFT)$ will be at least 0.5 or higher. \\ 44 45 In conclusion, we can calculate a worst case scenario with 150 \sw alerts per year and an overlap factor 46 of 0.5 yielding $N_{obs}^{min} \sim 0.6$/month. 47 An upper limit can be derived from 200 \sw alerts and a complete 48 overlap with $F_{overlap}(SWIFT) = 1$ yielding $N_{obs}^{max} \sim 1.6$/month. 28 49 29 50 \subsection{GRB observations in case of moon shine} … … 35 56 a fast moon-flash shouldn't damage the PMTs, but the behaviour 36 57 of the camera and the Camera Control {\it La Guagua} must 37 be tested. On the other hand, if such test conclude that it is not safe58 be tested. On the other hand, if such tests conclude that it is not safe 38 59 to get even a short flash from the moon, the possibility 39 60 to implement a new feature into the Steering System must be considered … … 43 64 44 65 There was a shift observing the Crab-Nebula with half-moon at La Palma in December 2004. 45 Th e experience wasthat the nominal HV could be maintained and gave no66 That experience showed that the nominal HV could be maintained and gave no 46 67 currents higher than 2\,$\mu$A. This means that moon-periods can be used for GRB-observations 47 68 without fundamental modifications except for full-moon periods. We want to stress that 48 69 these periods increase the chances to catch GRBs by 80\%. 49 It is therefore mandatory that the shifters keep the camera in fully operational conditions with high-voltages switched on from the beginning of a half-moon night until the end. This includes periods where no other half-moon observations are scheduled. If no other data can be taken during the this periond, the telescope shuld be pointed in the north direction, close to the zenith. This increase the probability to overlap with the FOV of the satellites. 70 It is therefore mandatory that the shifters keep the camera in fully operational conditions with 71 high-voltages switched on from the beginning of a half-moon night until the end. 72 This includes periods where no other half-moon observations are scheduled. 73 If no other data can be taken during the those periods, the telescope should be pointed 74 to a Northern direction, close to the zenith. This increases the probability to overlap 75 with the FOV of \sw. 50 76 51 77 \par 52 78 53 Because of higher background with moon-light, we suggest to decrease the maximu nzenith angle from54 $\theta_{max} = 70^\circ$ to $\theta_{max} = 65^\circ$ .79 Because of higher background with moon-light, we suggest to decrease the maximum zenith angle from 80 $\theta_{max} = 70^\circ$ to $\theta_{max} = 65^\circ$, there. 55 81 56 82 \subsection{Active Mirror Control behaviour} 57 83 58 To reduce the time before starting the observation, the use of the look-up tables (LUTs) is necessary. 59 Once generated, the {\it AMC} will use the LUTs and automaticaly focus the panels for a given telescope position. The {\it CC} should send the burst coordinates to the {\it Drive} and the {\it AMC} software in the same time. In this way the panels could be focussed already during the telescope movement. 84 To reduce the time before the start of the observation, the use of the look-up tables (LUTs) is necessary. 85 Once generated, the {\it AMC} will use the LUTs and automatically focus the panels for a given 86 telescope position. The {\it CC} should send the burst coordinates to the {\it Drive} and the {\it AMC} 87 software in the same time. In this way the panels could be focused already during the telescope movement. 60 88 61 89 \subsection{Calibration} … … 74 102 We determine the maximum zenith angle for GRB observations by requiring that the overwhelming majority of possible GRBs will have an in principle observable spectrum. Figure~\ref{fig:grh} 75 103 shows the gamma-ray horizon (GRH) as computed in~\cite{KNEISKE,SALOMON}. The GRH is defined as the 76 gamma-ray energy at which a part of $1/e$ of a hypothe siedmono-energetic flux gets absorbed after77 travelling a distance of $d$, expressed in redshift $z$ from the earth. One can see that at typical78 GRB distances of $z=1$, all gamma-rays above 100\,GeV get absorbed before they reach the earth.104 gamma-ray energy at which a part of $1/e$ of a hypothetical mono-energetic flux gets absorbed after 105 travelling a distance, expressed in redshift $z$, from the source. One can see that at typical 106 GRB distances of $z=1$, all gamma-rays above 100\,GeV get absorbed before they can reach the earth. 79 107 80 108 \par … … 107 135 \subsection{In case of follow-up: Next steps} 108 136 109 We propose to analy se the GRB data at the following day in order to tell whether a follow-up observation during the next night is useful. We think that a limit of 3\,$\sigma$ significance should be enough to start such a follow-up observation of the same place. This follow-up observation can then be used in two ways:137 We propose to analyze the GRB data at the following day in order to tell whether a follow-up observation during the next night is useful. We think that a limit of 3\,$\sigma$ significance should be enough to start such a follow-up observation of the same place. This follow-up observation can then be used in two ways: 110 138 111 139 \begin{itemize} … … 117 145 %%% mode: latex 118 146 %%% TeX-master: "GRB_proposal_2005" 147 %%% TeX-master: "GRB_proposal_2005" 119 148 %%% End:
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