Galactic stray light removal

The pickup of the Galactic signal through the sidelobes causes two kinds of systematic errors:

1. It introduces a bias in the calibration process. 2. It leaves a spurious signal in the calibrated map.

The first error is corrected including an estimate of the Galactic sidelobe pickup alongside the convolved dipole in the fit with the measured voltages. The beam pattern is decomposed into

[math]B_{main}+B_{sl}[/math],

and our estimate the gain [math]G[/math] is given through a linear least-squares fit between the voltages [math]V(t)[/math] and [math]T_{model}[/math] , defined as

[math]T_{model}=B\ast D+B_{sl}\ast T_{sky}. The term \lt math\gt B_{main}\ast T_{sky}[/math] is neglected in the fit because during the calibration we mask the Galactic plane, and we assume that the contribution to the fit given by the terms with [math]T_{CMB}[/math] is negligible.

The second error is corrected subtracting the residual signal caused by Galactic pickup through the sidelobes from the timelines immediately after calibration.