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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The high-energy diffuse cosmic gamma-ray background radiation from blazars

We predict the spectrum and flux of the high-energy diffuse cosmic gamma-ray background radiation produced by blazars. Our calculations are based on the Compton Observatory EGRET observations of high-energy gamma-rays from these objects, the Whipple observation of TeV gamma-rays from Mrk 421, and radio population studies of flat-spectrum radio sources. Our statistical analysis gives a result consistent with a linear correlation. We then use the radio luminosity function and redshift evolution to calculate the gamma-ray background. We find that blazars cannot account for the flux level or steep spectrum of the background observed by SAS 2 in the sub-GeV range, but could likely provide the dominant background component in the multi-GeV energy range and above. We predict a differential photon spectral index for this component of about 2 up to about 10 GeV. Above that energy, the spectrum should gradually steepen owing to pair production by interactions of the gamma-rays with intergalactic infrared photons. Using the calculations of this effect by Stecker et al. (1992), we estimate a spectral index of about 3.5 for energies above a TeV.

Stecker, F. W.↗
NASA NTRS1981

Large-angular-scale anisotropy in the cosmic background radiation

Results of an extended series of airborne measurements of large-angular-scale anisotropy in the 3-K cosmic background radiation are reported. A dual-antenna microwave radiometer operating at 33 GHz flown aboard a U-2 aircraft to 20-km altitude on 11 flights between December 1976 and May 1978 measured differential intensity between pairs of directions distributed over most of the Northern Hemisphere. Measurements show clear evidence of anisotropy that is readily interpreted as due to the solar motion relative to the sources of the radiation. The anisotropy is well fitted by a first order spherical harmonic of amplitude 3.6 + or - 0.5 mK, corresponding to a velocity of 360 + or - 50 km/s toward the direction 11.2 + or - 0.5 hours of right ascension and 19 deg + or - 8 deg declination.

Gorenstein, M. V.↗
NASA NTRS1994

Analysis of small-scale microwave background radiation anisotropy in the presence of foreground contamination

Many of the current round of experiments searching for anisotropies in the microwave background radiation (MBR) are confronting the problem of how to disentangle the cosmic signal from contamination due to Galactic and intergalactic foreground sources. Here we show how commonly used likelihood function techniques can be generalized to account for foreground. Specifically we set some restrictions on the spectrum of foreground contamination but allow the amplitude to vary arbitrarily. The likelihood function thus generalized gives reasonable limits on the MBR anisotropy which, in some cases, are not much less restrictive than what one would get from more detailed modeling of the foreground. Furthermore, the likelihood function is exactly the same as one would obtain by simply projecting out foreground contamination and looking at the reduced data set. We apply this generalized analysis to the recent medium-angle data sets of ACME-HEMT (Gaier et al. 1992; Schuster et al. 1993) and MAX (Meinhold et al. 1993; Gunderson et al. 1993). The resulting analysis constrains the one free parameter in the standard cold dark matter theory to be Q(sub rms-ps) = 18(sub -5 sup +8) microKelvin. This best fit value, although in striking agreement with the normalization from Cosmic Background Explorer (COBE), is not a very good fit, with an overall chi-squared/degrees of freedom = 208/168. We also argue against three commonly used methods of dealing with foreground: (1) ignoring it completely; (2) subtracting off a best-fit foreground and treating the residuals as if uncontaminated; and (3) culling data which appears to be contaminated by foreground.

Dodelson, Scott↗
NASA NTRS1978

Radiometer system to map the cosmic background radiation

A 33-GHz airborne radiometer system has been developed to map large angular scale variations in the temperature of the 3 K cosmic background radiation. A ferrite circulator switches a room-temperature mixer between two antennas pointing 60 deg apart in the sky. In 40 min of observing, the radiometer can measure the anisotropy of the microwave background with an accuracy of plus or minus 1 mK rms, or about 1 part in 3000 of 3 K. The apparatus is flown in a U-2 jet to 20 km altitude where 33-GHz thermal microwave emission from the atmosphere is at a low level. A second radiometer, tuned to 54 GHz near oxygen emission lines, monitors spurious signals from residual atmospheric radiation. The antennas, which have an extremely low side-lobe response of less than -65 dB past 60 deg, reject anisotropic radiation from the earth's surface. Periodic interchange of the antenna positions and reversal of the aircraft's flight direction cancel equipment-based imbalances. The system has been operated successfully in U-2 aircraft flown from NASA-Ames at Moffett Field, Calif.

Gorenstein, M. V.↗
NASA NTRS1976

Ionising flux of cosmic background radiation

The indirect method of estimating the diffuse metagalactic flux of ionizing radiation proposed by Sunyaev (1969) is reconsidered in the light of further studies of the interaction of this radiation with galactic gas. An upper limit is derived for the intensity of the metagalactic background radiation to which the neutral interstellar medium is exposed. This limit on the ionizing radiation flux severely restricts the emission from a galactic corona containing gas in the temperature range 100,000 to 1,000,000 K. An upper limit of 10 to the 29.2 erg/sec/Hz is obtained for the mean luminosity radiated by a quasar in the energy band 40-170 eV. The 21-cm observations examined indicate that further than about 30 kpc from the center of the galaxy self-shielding by H II is possible only when the critical metagalactic ionizing flux is not exceeded.

Silk, J.↗
NASA NTRS1981

Large-scale anisotropy of the cosmic microwave background radiation

Inhomogeneities in the large-scale distribution of matter inevitably lead to the generation of large-scale anisotropy in the cosmic background radiation. The dipole, quadrupole, and higher order fluctuations expected in an Einstein-de Sitter cosmological model have been computed. The dipole and quadrupole anisotropies are comparable to the measured values, and impose important constraints on the allowable spectrum of large-scale matter density fluctuations. A significant dipole anisotropy is generated by the matter distribution on scales greater than approximately 100 Mpc. The large-scale anisotropy is insensitive to the ionization history of the universe since decoupling, and cannot easily be reconciled with a galaxy formation theory that is based on primordial adiabatic density fluctuations.

Silk, J.↗
NASA NTRS1998

Anisotropy of the Cosmic Microwave Background Radiation on Large and Medium Angular Scales

This grant has supported work at Brown University on measurements of the 2.7 K Cosmic Microwave Background Radiation (CMB). The goal has been to characterize the spatial variations in the temperature of the CMB in order to understand the formation of large-scale structure in the universe. We have concurrently pursued two measurements using millimeter-wave telescopes carried aloft by scientific balloons. Both systems operate over a range of wavelengths, chosen to allow spectral removal of foreground sources such as the atmosphere, Galaxy, etc. The angular resolution of approx. 25 arcminutes is near the angular scale at which the most structure is predicted by current models to be visible in the CMB angular power spectrum. The main goal is to determine the angular scale of this structure; in turn we can infer the density parameter, Omega, for the universe as well as other cosmological parameters, such as the Hubble constant.

Houghton, Anthony↗
DOE OSTI2015

Background radiation measurements at high power research reactors

Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including γ-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. Furthermore, the general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1994

A measurement of the medium-scale anisotropy in the cosmic microwave background radiation

Observations from the first flight of the Medium Scale Anisotropy Measurement (MSAM) are analyzed to place limits on Gaussian fluctuations in the cosmic microwave background radiation (CMBR). This instrument chops a 30 min beam in a three-position pattern with a throw of +/- 40 min; the resulting data is analyzed in statistically independent single- and double-difference sets. We observe in four spectral channels at 5.6, 9.0, 16.5, and 22.5/cm, allowing the separation of interstellar dust emission from CMBR fluctuations. The dust component is correlated with the IRAS 100 micron map. The CMBR component has two regions where the signature of an unresolved source is seen. Rejecting these two source regions, we obtain a detection of fluctuations which match CMBR in our spectral bands of 0.6 x 10(exp -5) is less than Delta (T)/T is less than 2.2 x 10(exp -5) (90% CL interval) for total rms Gaussian fluctuations with correlation angle 0.5 deg, using the single-difference demodulation. Fore the double difference demodulation, the result is 1.1 x 10(exp -5) is less than Delta(T)/T is less than 3.1 x 10(exp -5) (90% CL interval) at a correlation angle of 0.3 deg.

Cheng, E. S.↗
NASA NTRS2004

Comparison of Measured Galactic Background Radiation at L-Band with Model

Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This paper presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometer Keywords-Galactic background, microwave radiometry; remote sensing;

LeVine, David M.↗
NASA NTRS1971

A search for spectral features in the submillimeter background radiation.

Mountaintop observations were made at 1 per cent spectral resolution of atmospheric and sky emission in an attempt to determine the spectral features of submillimeter background radiation. No emission features were found that could be related to the diffuse isotropic flux reported from rocket and balloon experiments.

Mather, J. C.↗
NASA NTRS1982

Maser radiometer for cosmic background radiation anisotropy measurements

A maser amplifier was incorporated into a low noise radiometer designed to measure large-scale anisotropy in the 3 deg K microwave background radiation. To minimize emission by atmospheric water vapor and oxygen, the radiometer is flown in a small balloon to an altitude to 25 km. Three successful flights were made - two from Palestine, Texas and one from Sao Jose dos Campos, Brazil. Good sky coverage is important to the experiment. Data from the northern hemisphere flights has been edited and calibrated.

Fixsen, D. J.↗
NASA NTRS2002

Diffuse Cosmic Infrared Background Radiation

The diffuse cosmic infrared background (CIB) consists of the cumulative radiant energy released in the processes of structure formation that have occurred since the decoupling of matter and radiation following the Big Bang. In this lecture I will review the observational data that provided the first detections and limits on the CIB, and the theoretical studies explaining the origin of this background. Finally, I will also discuss the relevance of this background to the universe as seen in high energy gamma-rays.

Dwek, Eli↗
NASA NTRS1985

A map of the cosmic background radiation at 3 millimeters

Data from a series of balloon flights covering both the Northern and Southern Hemispheres, measuring the large angular scale anisotropy in the cosmic background radiation at 3.3 mm wavelength are presented. The data cover 85 percent of the sky to a limiting sensitivity of 0.7 mK per 7 deg field of view. The data show a 50-sigma (statistical error only) dipole anisotropy with an amplitude of 3.44 + or - 0.17 mK and a direction of alpha = 11.2 h + or - 0.1 h, and delta = -6.0 deg + or - 1.5 deg. A 90 percent confidence level upper limit of 0.00007 is obtained for the rms quadrupole amplitude. Flights separated by 6 months show the motion of earth around the sun. Galactic contamination is very small, with less than 0.1 mK contribution to the dipole quadrupole terms. A map of the sky has been generated from the data.

Lubin, P.↗
DOE OSTI2011

Level crossing analysis of cosmic microwave background radiation: a method for detecting cosmic strings

In this paper we study the footprint of cosmic string as the topological defects in the very early universe on the cosmic microwave background radiation. We develop the method of level crossing analysis in the context of the well-known Kaiser-Stebbins phenomenon for exploring the signature of cosmic strings. We simulate a Gaussian map by using the best fit parameter given by WMAP-7 and then superimpose cosmic strings effects on it as an incoherent and active fluctuations. In order to investigate the capability of our method to detect the cosmic strings for the various values of tension, Gμ, a simulated pure Gaussian map is compared with that of including cosmic strings. Based on the level crossing analysis, the superimposed cosmic string with Gμ∼>4 × 10{sup −9} in the simulated map without instrumental noise and the resolution R = 1' could be detected. In the presence of anticipated instrumental noise the lower bound increases just up to Gμ∼>5.8 × 10{sup −9}.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

Gamma radiation background measurements from Spacelab 2

A Nuclear Radiation Monitor incorporating a NaI(Tl) scintillation detector was flown as part of the verification flight instrumentation on the Spacelab 2 mission, July 29 to August 6, 1985. Gamma-ray spectra were measured with better than 20 s resolution throughout most of the mission in the energy range 0.1 to 30 MeV. Knowledge of the decay characteristics and the geomagnetic dependence of the counting rates enable measurement of the various components of the Spacelab gamma-ray background: prompt secondary radiation, Earth albedo, and delayed induced radioactivity. The status of the data analysis and present relevant examples of typical background behavior are covered.

Paciesas, William S.↗
NASA NTRS1989

Gamma radiation background measurements from Spacelab 2

A Nuclear Radiation Monitor incorporating a NaI(Tl) scintillation detector was flown as part of the verification flight instrumentation on the Spacelab 2 mission, July 29 to August 6, 1985. Gamma-ray spectra were measured with better than 20 s resolution throughout most of the mission in the energy range 0.1 to 30 MeV. Knowledge of the decay characteristics and the geomagnetic dependence of the counting rates enable measurement of the various components of the Spacelab gamma-ray background: prompt secondary radiation, earth albedo, and delayed induced radioactivity. The status of the data analysis and present relevant examples of typical background behavior are covered.

Paciesas, William S.↗
NASA NTRS1987

Distortion of the cosmic background radiation by superconducting strings

Superconducting cosmic strings can be significant energy sources, keeping the universe ionized past the commonly assumed epoch of recombination. As a result, the spectrum of the cosmic background radiation is distorted in the presence of heated primordial gas via the Suniaev-Zel'dovich effect. Thiis distortion can be relatively large: the Compton y parameter attains a maximum in the range 0.001-0.005, with these values depending on the mass scale of the string. A significant contribution to y comes from loops decaying at high redshift when the universe is optically thick to Thomson scattering. Moreover, the isotropic spectral distortion is large compared to fluctuations at all angular scales.

Ostriker, J. P.↗