# Changeset 779

Ignore:
Timestamp:
May 4, 2001, 10:40:57 AM (20 years ago)
Message:
*** empty log message ***

File:
1 edited

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Unmodified
 r777 directed not to the position of the selected source but rather to a position which has a certain offset ($\Delta\beta$) from the source position. $\Delta\beta$ is taken as  ... degree in right ascension and every 20 minutes of observation the sign of $\Delta\beta$ is changed. The two wobble positions are called wobble-1 and wobble-2. There is no compelling reason to do the wobbling in right ascension rather than in any other direction. It also appears that this choice has no severe consequences for the analysis. Note that the sky region projected onto the camera is different for wobble positions 1 and 2. For fixed wobble position the sky region projected onto the camera remains the same during tracking of a source, although the sky image is rotating in the camera. The sky region projected onto the camera would not remain the same during tracking of a source, if $\Delta \beta$ were defined as a fixed angle in the local angles $\Theta$ or $\phi$. This would not necessarily be a disadvantage. In the case $\Delta \beta$ is taken as a fixed angle in $\phi$ a sky region would be selected whose center has the same zenith angle $\Theta$ as the source being observed. position. Every 20 minutes of observation the sign of $\Delta\beta$ is changed. The two wobble positions are called wobble position 1 and 2. $\Delta \beta$ may be chosen to be a direction difference in celestial coordinates (declination $\delta$, right ascension $\Phi$) or in local coordinates (zenith angle $\Theta$, azimuthal angle $\phi$). However the direction $\Delta \beta$ is defined, the sky region projected onto the camera is different for wobble positions 1 and 2. If $\Delta \beta$ is defined to be a direction difference in celestial coordinates, the sky region projected onto the camera for a fixed wobble position remains the same during tracking of a source, although the sky image is rotating in the camera. If $\Delta \beta$ is defined to be a direction difference in local coordinates, the sky region projected onto the camera is changing continuously during tracking of a source. The centers of the projected sky regions lie on a circle, which is centered at the source position. If $\Delta \beta$ is defined to be a direction difference in the local azimuthal angle $\phi$, the center of the camera and the source position would always have the same zenith angle $\Theta$. Since the reconstruction efficiency of showers mainly depends on $\Theta$, this may be an advantage of defining $\Delta \beta$ in this way. The wobble mode has to be understood as an alternative to taking on- that one is taking on-data only, from which also the 'off-data' have to be obtained by some procedure. Open questions : - how should $\Delta \beta$ be defined - how big should $\Delta \beta$ be chosen \item Pedestals :\\ \begin{thebibliography}{xxxxxxxxxxxxxxx} \bibitem{fegan96}D.J.Fegan, Space Sci.Rev. 75 (1996)137 \bibitem{hillas85}A.M.Hillas, Proc. 19th ICRC, La Jolla 1 (1985) 155 \bibitem{hillas85}A.M.Hillas, Proc. 19th ICRC, La Jolla 3 (1985) 445 \bibitem{konopelko99}A.Konopelko et al., Astropart. Phys. 10 (1999) 275