No abstract

The photometric errors of the external calibrator for the FIRAS instrument on the COBE are smaller than the measurement errors on the cosmic microwave background (CMBR) spectrum (typically 0.02 MJy/sr, 1 σ), and smaller than 0.01% of the peak brightness of the CMBR. The calibrator is a re-entrant cone, shaped like a trumpet mute, made of Eccosorb iron-loaded epoxy. It fills the entire beam of the instrument and is the source of its accuracy. Its known errors are caused by reflections, temperature gradients, and leakage through the material and around the edge.Estimates and limits are given for all known error sources. Improvements in understanding the temperature measurements of the calibrator allow an improved CMBR temperature determination of 2.725±0.002 K.

No abstract

We present a determination of the cosmic microwave background dipole amplitude and direction from the COBE Di erential Microwave Radiometers (DMR) rst year of data. Data from the six DMR channels are consistent with a Dopplershifted Planck function of dipole amplitude T = 3:365 0:027 mK toward direction (l II ; b II ) = (264:4 0:3 ; 48:4 0:5 ). The implied velocity of the Local Group with respect to the CMB rest frame isṽ LG = 627 22 km s 1 toward (l II ; b II ) = (276 3 ; 30 3 ). DMR has also mapped the dipole anisotropy resulting from the Earth's orbital motion about the Solar system barycenter, yielding a measurement of the monopole CMB temperature T 0 at 31.5, 53, and 90 GHz, T 0 = 2:75 0:05 K. Subject headings: cosmic microwave background | cosmology: observations 2

No abstract