The Cosmic Microwave Background Spectrum from the Full COBE FIRAS Data Set

We have refined the analysis of the data from the FIRAS (Far-InfraRed Absolute Spectrophotometer) on board the COBE (COsmic Background Explorer). The FIRAS measures the difference between the cosmic microwave background and a precise blackbody spectrum. We find new, tighter upper limits on general deviations from a blackbody spectrum. The rms deviations are less than 50 parts per million of the peak of the cosmic microwave background radiation. For the Comptonization and chemical potential, we find |y| <15 x 10^-6 and |μ| <9 x 10^-5 (95% confidence level [CL]). There are also refinements in the absolute temperature, 2.728±0.004 K (95% CL), the dipole direction, (l, b) = (264°.14 + 030 48°.26±0.30) (95% CL), and the amplitude, 3.372 + 0.014 mK (95% CL). All of these results agree with our previous publications.