The power-law behaviours of angular spectra of polarized Galactic synchrotron

We study the angular power spectra of polarized Galactic synchrotron in the range 10 I :! 800, at several frequencies between 0.4 and 2.7 GHz and at several Galactic latitudes up to near the North Galactic Pole. Electric- and magnetic-parity polarization spectra are found to have slopes around alpha(E,B) = 1.4-1.5 in the Parkes and Effelsberg Galactic-Plane surveys, but strong local fluctuations of alpha(E,B) are found at \b\ similar or equal to 10degrees from the 1.4 GHz Effelsberg survey. The C-PH spectrum, which is insensitive to the polarization direction, is somewhat steeper, being alpha(PI) = 1.6-1.8 for the same surveys. The low-resolution multifrequency survey of Brouw and Spoelstra [A&AS 26 (1976) 129] shows some flattening of the spectra below I GHz, more intense for C-E,C-BI than for C-PH. In no case we find evidence for really steep spectra. The extrapolation to the cosmological window shows that at 90 GHz the detection of E-mode harmonics in the cosmic background radiation should not be disturbed by synchrotron, even around 1 similar or equal to 10 for a reionization optical depth tau(ri) greater than or similar to 0.05. (C) 2002 Elsevier Science B.V. All rights reserved.