An analysis of recent measurements of the temperature of the cosmic microwave background radiation

This paper presents an analysis of the results of recent temperature measurements of the cosmic microwave background radiation (CMBR). The observations for wavelengths longer than 0.1 cm are well fitted by a blackbody spectrum at 2.74 ± 0.02 K; however, including the new data of Matsumoto et al the result is no longer consistent with a Planckian spectrum. The data are described by a Thomson-distortion parameter u = 0.020 ± 0.002 and temperature 2.813 + 0.010 K at the 68% confidence level. Fitting the low-frequency data to a Bose-Einstein spectral distortion yields a 95% confidence level upper limit of 1.4 × 10^-2 on the chemical potential μ₀. These limits on spectral distortions place restrictions on a number of potentially interesting sources of energy release to the CMBR, including the hot intergalactic medium proposed as the source of the X-ray background.