C. Witebsky

New 33 GHz Measurements of the Cosmic Background RadiationIntensity

LBL-19323 Preprint LB Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Physics Division p. •Mr.£ Submitted t o The A s t r o p h y s i c a l J o u r n a l NEW 33 GHz MEASUREMENTS OF THE COSMIC BACKGROUND RADIATION INTENSITY G. De A m i c i , G. Smoot, S.D. and C. Witebsky March Friedman, TWO-WEEK This which is a Library may LOAN Circulating be borrowed COPY Copy for two weeks. Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098

Low-Frequency Measurements of the Cosmic Background Radiation Spectrum

The long-wavelength spectrum of the cosmic background radiation has been measured at five wavelengths (0.33, 0.9, 3.0, 6.3, and 12.0 cm). These measurements represent a continuation of the work reported by Smoot et al. (1983). The combine results have a weighted average of 2.73 {+-} 0.05 K and are consistent with past measurements. They limit the possible Compton distortion of the Cosmic Background Radiation spectrum to less than 8%.

THE GEM PROJECT: AN INTERNATIONAL COLLABORATION TO SURVEY GALACTIC RADIATION EMISSION

The GEM (Galactic Emission Mapping) project is an international collaboration established with the aim of surveying the full sky at long wavelengths with a multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz were completed from an Equatorial site in Colombia. The observations cover the celestial band 0h<α<24h, and −24° 22′<δ<+35° 37′. Preliminary results of this partial survey will be discussed. A review of the instrumental setup and a ∼10° resolution sky map at 408 MHz is presented.

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 fit by a blackbody spectrum at 2.74 {+-} 0.02 K; however, including the new data of Matsumoto et al. (1987) the result is no longer consistent with a Planckian spectrum. The data are described by a Thomson-distortion parameter u = 0.021 {+-} 0.002 and temperature 2.823 {+-} 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 x 10{sup -2} on the chemical potential {mu}{sub 0}. 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.

A measurement of the temperature of the cosmic microwave background at a frequency of 7.5 GHz

LBL-27451 Preprint Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Physics Division For Reference R r- z \ v E D Not to be Submitted to Astrophysical Journal isk^al&afaeMm OCT 0 1909 U3KARY AND DOCUMENTS SECTION A Measurement of the Temperature of the Cosmic Microwave Background at a Frequency of 7.5 GHz A. Kogut, M . Bensadoun, G. De Amici, S. Levin, G.F. Smoot, and C. Witebsky June 1989 Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098.

The temperature of the cosmic microwave background radiation at a frequency of 10 GHz

We have measured the temperature of the cosmic microwave background radiation (CMBR) at a frequency of 10 GHz (wavelength 3.0 cm) as part of a larger effort to determine the spectrum of the CMBR in the Rayleigh-leans region. The instrument used is a superheterodyne Dicke-switched radiometer. We have repeated the measurement over four summers with successively improved techniques and equipment. Our best estimate of the CMBR thermodynamic temperature at 10 GHz is 2.61 ± 0.06 K, where the error estimate is a 68% confidence level limit. Subject headings: cosmic background radiation ..

Effects of Atmospheric Emission on Ground-based Microwave Background Measurements

We present an analysis of multifrequency measurements ofatmospheric emission in the Rayleigh-Jeans portion of the cosmicmicrowave background spectrum (1-90 GHz) taken since 1986 from WhiteMountain, CA, and from the South Pole. Correlations of simultaneous dataat 10 and 90 GHz and accurate low-frequency measurements show goodagreement with model predictions for both sites. Our data from the SouthPole 1989 campaign combined with real-time measurements of the localatmospheric profiles provide accurate verification of the expectedindependent contributions of H2O and O2 emission. We show that variationson the order of 10 percent of the oxygen emission (both resonant andnonresonant components) are present on timescales of hours to days,mainly due to the evolution of the atmospheric pressure profile. Oxygenemission fluctuations appear larger than previously expected and may havesignificant consequences for ground-based cosmic microwave backgroundexperiments.

A large L-band rectangular corrugated horn

A lightweight, rectangular, corrugated-horn antenna constructed from sheet metal is described. Over a 1.3-1.7 GHz operating band, its half-power beamwidth is approximately 20\deg in the E -plane and varies from 17\deg to 13\deg in the H -plane. Quarter-wave choke slots at the aperture help to reduce the E -plane sidelobes below -55 dB at angles greater than 90\deg , while the H -plane sidelobes lie in that range both with and without choke slots. Return loss throughout the operating band is -25 dB or below. Critical dimensions are provided, together with useful guidelines for designing similar antennas.

New measurements of the cosmic background radiation temperature at 3. 3 millimeter wavelength

We have measured the temperature of the cosmic background radiation (CBR) at 3.3 mm wavelength in 1982, 1983, and 1984 as part of a larger project to determine the CBR temperature at five wavelengths from 12 cm to 3.3 mm (Smoot et al. 1985). The 3.3-mm measurements yield a brightness temperature of 2.57 K with a 1{sigma} uncertainty of 20.12 K. This paper describes the instrument, the measurement techniques, and the data-analysis procedures used. Our result is in good agreement with recent measurements at comparable wavelengths by Meyer and Jura (1985) and by Peterson, Richards, and Timusk (1985), but it disagrees with the temperatures reported by Woody and Richards (1981).

A Liquid-Helium-Cooled Absolute Reference Cold Load for Long-Wavelength Radiometric Calibration

We describe a large (78-cm) diameter liquid-helium-cooled black-body absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid helium (LHe) boiling point, accurate to better than 30 mK for wavelengths from 2.5 to 25 cm (12-1.2 GHz). The emission (from non-LHe temperature parts of the cold load) and reflection are small and well determined. Total corrections to the LHe boiling point temperature are {le} 50 mK over the operating range. This cold load has been used at several wavelengths at the South Pole and at the White Mountain Research Station. In operation, the average LHe loss rate was {le} 4.4 l/hr. Design considerations, radiometric and thermal performance and operational aspects are discussed. A comparison with other LHe-cooled reference loads including the predecessor of this cold load is given.