Cosmic Background Explorer/FIRAS
CMB Monopole Spectrum
Fixsen et al. (1996) modeled the full FIRAS low-frequency calibrated sky spectra as a superposition of a CMB monopole, a CMB dipole and selected Galactic emission components. Table 4 of their paper gives the residuals of the derived CMB monopole spectrum from a perfect blackbody. Subsequent analyses by Mather et al. (1999) and Fixsen et al. (2002) improved the FIRAS calibration accuracy and provided a best-estimate for the absolute CMB temperature of 2725 +/- 1 mK.
The CMB monopole spectrum posted here is the sum of a 2.725 K blackbody spectrum and the residual intensity noted above. The complete contents of Table 4 are also provided, in the form of the original residuals, 1-sigma uncertainties, and the modeled Galaxy spectrum.
More details can be found in:
"The Spectral Results of the Far-Infrared Absolute Spectrophotometer
Instrument on COBE"