SPIDER: probing the early Universe with a suborbital polarimeter

Abstract

We evaluate the ability of SPIDER, a balloon-borne polarimeter, todetect a divergence-free polarization pattern (B-modes) in thecosmic microwave background (CMB). In the inflationary scenario, theamplitude of this signal is proportional to that of the primordialscalar perturbations through the tensor-to-scalar ratio r. We showthat the expected level of systematic error in the SPIDER instrumentis significantly below the amplitude of an interesting cosmologicalsignal with r = 0.03. We present a scanning strategy that enables usto minimize uncertainty in the reconstruction of the Stokes parametersused to characterize the CMB, while accessing a relatively wide rangeof angular scales.Evaluating the amplitude of the polarized Galacticemission in the SPIDER field, we conclude that the polarized emissionfrom interstellar dust is as bright or brighter than the cosmologicalsignal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), asituation similar to that found in the ``Southern Hole.'' We showthat two ∼ 20-day flights of the SPIDER instrument canconstrain the amplitude of the B-mode signal to r < 0.03 (99% CL)even when foreground contamination is taken into account. In theabsence of foregrounds, the same limit can be reached after one 20-dayflight.