N. Ponthieu March 30th, A few thoughts on scanning strategy F. R. Bouchet, M. Bucher, F. X. Désert, N. Ponthieu, M. Piat

N. Ponthieu March 30th, Polarized map making in principle Solution : Covariance matrix of I, Q, U Redundancy together with angular homogeneity impact on the S/N + IQU decorrelation Minimum An intuitive estimator of the quality of the pointing is

N. Ponthieu March 30th, Polarization systematics mitigation The main systematic effects are not spin-2 quantities, so they average out if the angular coverage is homogeneous Especially true for the most ‘’serious’’ ones like differential gain Can gain 1 order of magnitude in rejection between two scanning strategies Hu et al, 2004 Ponthieu & Hivon, 2007 in prep Scanning strategy is the first tool for systematic mitigation

N. Ponthieu March 30th, Example: WMAP Short term redundancy on all angular scales Good angular redundancy on most of the sky

N. Ponthieu March 30th, Examples: parameterization Planck –  = 85 deg, T spin = 60 sec – a = 10 deg, T prec = 6 months EPIC/JPL –  = 45 deg, T spin = 63 sec – a = 50 deg, T prec = 3.2 h WMAP Planck EPIC

N. Ponthieu March 30th, Exploring the parameter space Trajectory of one pixel on the sky

N. Ponthieu March 30th, Exploring the parameter space Parameters:  3 angles  3 rotation speeds Goal:  Short term redundancy on all angular scales  Large fraction of the sky covered in a few days  Good angular coverage  Jacknife possibilities some constraints  The scan speed of the line of sight must be compatible with the beam, the detector time constant  The sampling rate must be compatible with the telemetry (if no onboard aggressive data compression)  Cope with thermal effects, solar pannels orientation, SCAO etc… Example of set of parameters:  = 45  = 45 T  = sec T  = 2400 sec T  = 20 sec

N. Ponthieu March 30th, day, detector at r/3 (  =2.5deg) N hits cos2 

N. Ponthieu March 30th, days, detector at r/3 (  =2.5deg) N hits cos2 

N. Ponthieu March 30th, days, detector at r/3 (  =2.5deg) N hits cos2 

N. Ponthieu March 30th, Figures of merit Redundancy and homogeneity Want some more deeply integrated regions to really dig into systematics ? Calibration ? How deep do we want to integrate vs how much sky do we want to cover in the same amount of time ? … etc… At this stage of the study, we did not have to quantify exactly the benefit from a particular set of parameters. But we did find one that is feasible and meets the constraints we set.

N. Ponthieu March 30th, Conclusion Scanning strategy is essential to sensitivity It is the first tool to mitigate systematic effects Is is a powerful tool It is a strong driver of the mission architecture non homogeneous sky coverage compromises E/B separation It will be a strong driver of the data analysis, compression…? Cf. Radek’s talk