The Cosmic Microwave Background Spectrum from the Full<i>COBE</i>FIRAS Data Set

TLDR

FIRAS measures the difference between the cosmic microwave background and a precise blackbody spectrum. The authors refined the analysis of FIRAS data from the COBE mission. The refined analysis yields tighter upper limits on deviations from a blackbody spectrum, with rms deviations below 50 ppm, |y| < 15 × 10⁻⁶, |μ| < 9 × 10⁻⁵, and updated values for the CMB temperature (2.728 ± 0.004 K), dipole direction, and amplitude, all consistent with prior results.

Abstract

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 × 10–6 and |μ| < 9 × 10–5 (95% confidence level [CL]). There are also refinements in the absolute temperature, 2.728 ± 0.004 K (95% CL), the dipole direction, (1, b)/(26414 ± 0.30, 4826 ± 0.30) (95% CL), and the amplitude, 3.372 ± 0.014 mK (95% CL). All of these results agree with our previous publications.