Wobbler switching

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Wobbler switching

In case of wobbler switching, the LONGOFF and LATOFF columns describe the primary dish direction on sky. Because the secondary mirror switches with additional offsets between the ON and OFF positions, MRTCAL assumes that the ON phases always have (0,0) antenna offsets. For simplicity, the OFF phases offsets are also set to (0,0) (instead of ) but the CLASS switching section will describe properly the throw when saving the ON-OFF result, or when saving the ON and OFF separately. Remember that the wobbler throw is usually along azimuth with a given projection, while the CLASS offsets are described in equatorial or galactic system with radio projection: their addition is not straightforward.

Figure: Asymmetrical wobbler switching illustration. For each subscan, the antenna (primary dish) points at away from the source, usually in the azimuthal direction (blue line). This is called antenna noding. During the subscan, the secondary mirror switches (red line) from the ON position (at offset 0) to one OFF position (at offset ). is the wobbler throw. This pattern, which alternates between OFF1 and OFF2 at each subscan, is called asymmetrical wobbler switching, as opposed to the symmetrical wobbler switching (see details in Fig ).

Figure: Symmetrical wobbler switching illustration. Same as Fig , except that the subscans are observed with symmetry around a given time. Thanks to this, and assuming that the atmospheric properties drift linearly through time, the atmospheric variations between the 2 OFF1 subscans and between the 2 OFF2 subscans average at the same level.