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The scattering and absorption of electromagnetic waves by a spherically symmetric nonrotating black hole is studied in the Schwarzschild background, by means of the known expansion of the modified Debye potentials in partial waves. The power reflection coefficients and the phase shifts of the partial waves are evaluated at both high and low frequencies. Then the scattering and absorption cross sections of the black hole are determined. It is shown that the black hole is almost unable to absorb electromagnetic waves when the wavelength of the radiation is greater than the Schwarzschild radlus.

We study the angular power spectra of polarized Galactic synchrotron in the range 10 < ∼ l ≤ 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 α E,B = 1.4 − 1.5 in the Parkes and Effelsberg Galactic-Plane surveys, but strong local fluctuations of α E,B are found at |b| ≃ 10 • from the 1.4 GHz Effelsberg survey. The C P Il spectrum, which is insensitive to the polarization direction, is somewhat steeper, being α P I = 1.6 − 1.8 for the same surveys. The low-resolution multifrequency survey of Brouw and Spoelstra (1976) shows some flattening of the spectra below 1 GHz, more intense for C E,Bl than for C P Il . 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 l ≃ 10 for a reionization optical depth τ ri > ∼ 0.05.

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We derive the angular power spectra of intensity and polarization of Galactic synchrotron emission in the range 36 < l < 10^3 from the Parkes survey mapping the southern Galactic plane at 2.4 GHz. The polarization spectra of both electric and magnetic parity up to l \simeq 10^3 are approximated very well by power laws with slope coefficients \simeq 1.4, quite different from the CMB spectra. We show that no problem should arise from Galactic synchrotron for measurements of CMB polarization in the cosmological window.Comment: 15 pages with 6 eps figures. Accepted for publication in New Astronom