Short
Talk
Abstract :Future Cosmic Microwave Background (CMB) satellite missions aim to use the $B$ mode
polarization to measure the tensor-to-scalar ratio $r$ with a
sensitivity $\sigma_r \ltorder 10^{-3}$. Achieving this goal will not
only require sufficient detector array sensitivity but also
unprecedented control of all systematic errors inherent to CMB
polarization measurements. Since polarization measurements derive from
differences between observations at different times and from different
sensors, detector response mismatches introduce leakages from intensity
to polarization and thus lead to a spurious $B$ mode signal. Because
the expected primordial $B$ mode polarization signal is dwarfed by the
known unpolarized intensity signal, such leakages could contribute
substantially to the final error budget for measuring $r.$ Using
simulations we estimate the magnitude and angular spectrum of the
spurious $B$ mode signal resulting from bandpass mismatch between
different detectors. It is assumed here that the detectors are
calibrated, for example using the CMB dipole,so that their sensitivity
to the primordial CMB signal has been perfectly matched. Consequently
the mismatch in the frequency bandpass shape between detectors
introduces differences in the relative calibration of galactic emission
components. We simulate this effect using a range of scanning patterns
being considered for future satellite missions. We find that the
spurious contribution to $r$ from reionization bump on large angular
scales ($\ell < 10$) is $\approx 10^{-3}$ assuming large detector
arrays and 20 percent of the sky masked. We show how the amplitude of
the leakage depends on the angular coverage per pixels that results
from the scan pattern.
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