Engineering topics

Boughn, S. P.

Publications and source records attributed to Boughn, S. P..

6 records

NASA NTRS1998

Correlations Between the Cosmic X-Ray and Microwave Backgrounds: Constraints on a Cosmological Constant

In universes with significant curvature or cosmological constant, cosmic microwave background (CMB) anisotropies are created very recently via the Rees-Sciama or integrated Sachs-Wolfe effects. This causes the CMB anisotropies to become partially correlated with the local matter density (z less than 4). We examine the prospects of using the hard (2- 10 keV) X-ray background as a probe of the local density and the measured correlation between the HEAO1 A2 X-ray survey and the 4-year COBE-DMR map to obtain a constraint on the cosmological constant. The 95% confidence level upper limit on the cosmological constant is OMega(sub Lambda) less than or equal to 0.5, assuming that the observed fluctuations in the X-ray map result entirely from large scale structure. (This would also imply that the X-rays trace matter with a bias factor of b(sub x) approx. = 5.6 Omega(sub m, sup 0.53)). This bound is weakened considerably if a large portion of the X-ray fluctuations arise from Poisson noise from unresolved sources. For example, if one assumes that the X-ray bias is b(sub x) = 2, then the 95% confidence level upper limit is weaker, Omega(sub Lambda) less than or equal to 0.7. More stringent limits should be attainable with data from the next generation of CMB and X-ray background maps.

Boughn, S. P.↗

NASA NTRS1993

A comparison of the cosmic microwave and cosmic X-ray backgrounds - Constraints on local sources of the fluctuations observed by COBE

It has been suggested by Hogan (1992) that the microwave background anisotropy detected by the COBE DMR experiment (Smoot et al., 1992) might be produced by inverse Compton scattering from hot diffuse clouds of electrons in nearby superclusters. If the COBE fluctuations are due to this mechanism, then the absence of anticorrelations between maps of the cosmic microwave and cosmic X-ray backgrounds constrains the temperature (16 keV) and density (less than 2 x 10 exp -6/cu cm) of the ionized supercluster gas. Since the COBE limits on spectral distortion indicate that the temperature of the intergalactic medium is less than 10 keV, we conclude that the fluctuations observed by COBE are probably not produced by this mechanism.

Boughn, S. P.↗

NASA NTRS1992

Limits of Gaussian fluctuations in the cosmic microwave background at 19.2 GHz

The Northern Hemisphere data from the 19.2 GHz full sky survey are analyzed to place limits on the magnitude of Gaussian fluctuations in the cosmic microwave background implied by a variety of correlation functions. Included among the models tested are the monochromatic and Gaussian-shaped families, and those with power-law spectra for n values between -2 and 1. An upper bound is placed on the quadrupole anisotropy of Delta T/T less than 3.2 x 10 exp -5 rms, and an upper bound on scale-invariant (n = 1) fluctuations of a2 less than 4.5 x 10 exp -5 (95 percent confidence level). There is significant contamination of these data from Galactic emission, and improvement of the modeling of the Galaxy could yield a significant reduction of these upper bounds.

Boughn, S. P.↗

NASA NTRS1991

Limits on Gaussian fluctuations in the cosmic microwave background at 19.2 GHz

The Northern Hemisphere data from the 19.2 GHz full sky survey are analyzed to place limits on the magnitude of Gaussian fluctuations in the cosmic microwave background implied by a variety of correlation functions. Included among the models tested are the monochromatic and Gaussian-shaped families, and those with power law spectra for n from -2 to 1. We place an upper bound on the quadrupole anisotropy of DeltaT/T less than 3.2 x 10 exp -5 rms, and an upper bound on scale-invariant (n = 1) fluctuations of a2 less than 4.5 x 10 exp -5 (95 percent confidence level). There is significant contamination of these data from Galactic emission, and improvement of our modeling of the Galaxy could yield a significant reduction of these upper bounds.

Boughn, S. P.↗

NASA NTRS1990

A balloon borne 19-GHz radiometer

The design and performance of a 19-GHz one-horn maser radiometer is discussed. The antenna is a lensed, conical horn with 3-deg angular resolution. The radiometer is stabilized by chopping against an internal cold load. A novel chopping scheme allows continual calibration of maser gain fluatuations with only a modest penalty in noise. The method of calibrating this instrument is described. The instrument has been used to map the sky with an equivalent blackbody temperature sensitivity of 1 mK per 3 x 3 deg resolution element.

Boughn, S. P.↗

NASA NTRS1981

Dipole and quadrupole anisotropy of the 2.7 K radiation

Results of measurements of the dipole and quadrupole anisotropy of the microwave background radiation are reported. Balloon-borne measurements of the temperature difference between two horn antennas pointed 90 deg apart and 45 deg from the zenith were carried out at frequencies of 24.8, 31.4 and 46.0 GHz to determine three dipole and four quadrupole parameters. When combined with data from two previous balloon flights, a dipole anisotropy of 3.78 + or - 0.30 mK in the direction 11.6 + or - 0.2 h RA, -12 + or - 5 deg dec is obtained. The measurements reveal a spectral index of 0.04 + or - 0.28 between 19.0 and 46.0 GHz, indicating that the dipole effect arises from an intrinsic anisotropy in the temperature of the background and/or a first-order Doppler shift due to solar motions. A statistically significant quadrupole effect is also detected which is attributed to the intrinsic anisotropy of the 2.7 K background.

Boughn, S. P.↗