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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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NASA NTRS1991

Late time cosmological phase transitions 1: Particle physics models and cosmic evolution

We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.

Frieman, Joshua A.↗
NASA NTRS2023

Testing theories of Gravitation with the Interstellar Probe Radio Experiment

General Relativity (GR) will soon celebrate its 110th birthday, holding up against all experimental enquiry. Nonetheless, unification theories attempting to quantize gravity, such as string theory, are gaining footing. These hypothesize additional scalar, vector, and tensor long-range fields that couple to matter (Will, 2014), introducing violations to GR. Although such violations have never been detected, it is likely that GR will not be the ultimate theory of gravity. What is certain is that gravity tests are alive and well, pushing the validity of GR to new scales and accuracies, or -potentially- suggesting alternative routes for new physics. Building upon the legacy of Voyager and Pioneer missions, which demonstrated the capability to survive in the outer reaches of the solar system, the Interstellar Probe mission concept (McNutt et al., 2022) aims to characterise our heliosphere through state-of-the-art instrumentation, opening new frontiers also for GR testing. In this work, we investigate the possibility of constraining the Nordtvedt parameter η and the mass of the graviton via the Compton wavelength λc, by simulating the processing of 10 years of radiometric data from the Interstellar Probe. Station calibration and clock synchronisation, as well as limiting spacecraft precession manoeuvres are highlighted as key strategies for obtaining high-quality estimates. In the most favourable scenario, η can be constrained to less than 1.5 · 10 -5 , reducing the uncertainty obtained via Lunar Laser Ranging (Hofmann and Müller, 2018), and a lower bound of 1.4 ‧ 10 14 km is set for λc, improving the estimates obtained from planetary ephemerides (Bernus et al., 2020) and gravitational wave detection (Abbott et al., Jun 2021). Extending ranging measurement acquisition to 20 years improves the results tenfold. This experiment interrogates fundamental physics from a unique dynamical setting, investigating possible violations of the Equivalence Principle (EP) underlying GR.

general relativity↗
NASA NTRS1982

An 80 day X-ray light curve of 3C 371

The Large Area Sky Survey (LASS) experiment on HEAO 1 that monitored the N galaxy/BL Lacertae object 3C 371 from August 19 to November 7, 1977 is discussed, noting that statistically significant threefold or larger intensity variations were observed in the flux range 0.5-20 keV. It is found that the degree of variability depends on the time of observation, with the source sometimes appearing constant and sometimes changing on time scales of 1 to 2 weeks. Also observed was an X-ray flare that lasted approximately 25 days. The total 80-day X-ray light curve is seen as suggesting either a superposition of X-ray flares or a variable injection rate that changes on weekly time scales. The observed X-ray flux is found to be consistent with that expected by extrapolating the nonthermal optical spectrum, suggesting that the optical to X-ray flux could be synchrotron radiation, provided that it is possible to account for the patterns of variability seen at optical and X-ray wavelengths and to dispose of inverse Compton difficulties.

Snyder, W. A.↗
NASA NTRS1994

X-ray spectra of a complete sample of extragalactic core-dominated radio sources

We present ROSAT soft X-ray spectra for the members of a complete sample of 13 core-dominated, flat radio spectrum sources. The sample comprises all radio sources from a flux-limited radio catalog (S(sub 5GHz) greater than 1 Jy; Kuehr et al. 1981) which are north of delta = 70 deg, at galactic latitudes b greater than 10 deg, and have a flat radio spectrum between 1.4 and 5 GHz (alpha(sub r) less than 0.5; f approximately nu(sup -alpha)). The sources have already undergone much study at radio and optical wavelengths and are classified in broad terms as quasars (8 sources) and BL Lac objects (5 sources). We find mean X-ray power-law energy indices of alpha(sub x) = 0.59 +/- 0.19 for the quasars and 1.36 +/- 0.27 for the BL Lac objects (68% confidence range for two parameters of interest as determined by a maximum likelihood method), supporting earlier Einstein Observatory results for heterogeneous samples of sources (Worrall & Wilkes 1990). A non-zero dispersion on alpha(sub x) is found for both the quasars and the BL Lac objects. When we incorporate published radio, mm, and optical measurements and compare the X-ray and broad-band spectral indices alpha(sub x), alpha(sub rx), alpha(sub mm,x), and alpha(sub ox), the most obvious difference between the quasar and BL Lac subsamples lies within the X-ray band. We have fitted the multi-wavelength data to inhomogeneous synchotron-self-Compton models and find that, for the BL Lac objects with steep X-ray spectra, synchotron emission can account for the radio to soft X-ray measurements, whereas the BL Lac objects with hard X-ray spectra and the quasars require significant Compton emission to model the spectral flattening indicated by alpha(sub x) less than alpha(sub ox).

Brunner, H.↗
NASA NTRS2002

The Sunyaev-Zel'dovich Effect Spectrum of Abell 2163

We present an interferometric measurement of the Sunyaev-Zel'dovich effect (SZE) at 1 cm for the galaxy cluster Abell 2163. We combine this data point with previous measurements at 1.1, 1.4, and 2.1 mm from the SuZIE experiment to construct the most complete SZE spectrum to date. The intensity in four wavelength bands is fit to determine the Compton y-parameter (y(sub 0)) and the peculiar velocity (v(sub p)) for this cluster. Our results are y(sub 0) = 3.56((sup +0.41+0.27)(sub -0.41-0.19)) X 10(exp -4) and v(sub p) = 410((sup +1030+460) (sub -850-440)) km s(exp -1) where we list statistical and systematic uncertainties, respectively, at 68% confidence. These results include corrections for contamination by Galactic dust emission. We find less contamination by dust emission than previously reported. The dust emission is distributed over much larger angular scales than the cluster signal and contributes little to the measured signal when the details of the SZE observing strategy are taken into account.

LaRoque, S. J.↗
NASA NTRS1991

The Galactic center radio source shines below the Compton limit

Absence of refractive scintillation of Sgr A*, the Galactic center radio source, at 1.3 and 0.8 mm wavelengths places an observational limit of brightness temperature of below 0.5 x 10 exp 12 K on the source. This is less than the maximum brightness of an incoherently synchrotron-emitting plasma, 10 exp 12 K, known as the Compton limit. The refractive scintillations expected, due to strong broadening of the source by the interstellar plasma, are observed by Zhao et al. at decimeter wavelengths. It has proven to be impossible to observe them at 1.3 and 0.8 mm wavelengths over time spans between 0.1 s and 24 hr. Such scintillations are quenched by source size greater than about 0.1 AU, or, equivalently, less than 0.5 x 10 exp 12 K for Sgr A*, at 0.8 mm wavelength. The scintilations would also require fluctuations with scale sizes of 0.1 AU in the scattering plasma, moving across the line of sight at velocities above about 100 km/s. The plasma that scatters Sgr A* satisfies the latter two conditions, and the absence of scintillations is due to the size of the source. This observation strengthens the identification of Sgr A* as a quiescent galactic nucleus.

Gwinn, C. R.↗
NASA NTRS1984

Coordinated multifrequency observations of the BL Lacertae objects Mrk 180 and Mrk 501

The continuous spectra of the nearby BL Lac objects Mrk 180 and Mrk 501 have been investigated by making coordinated observations at X-ray, ultraviolet, optical, and radio wavelengths. The observations were planned in order to obtain single-epoch snapshots, or time-frozen spectra, of the emission at many different wavelengths. The spectra were fitted with spherically symmetric, synchrotron self-Compton models and relativistic jet models with relaxed assumptions of spherical geometry and homogeneity and allowance for relativistic motion. It is found that these models provide accurate fits to the observed spectra and tighter constraints on the physical parameters. These models are also not dependent on uncertain source size and synchrotron break frequency.

Mufson, S. L.↗
NASA NTRS1994

Ultraviolet observations of the gamma-ray blazer 3C 279 following the gamma-ray flare of 1991 June

Ultraviolet observations of the gamma-ray balzar 3C 279 were carried out in 1991 July with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy Energetic Gamma Ray Experiment Telescope (EGRET) instrument aboard the Compton Gamma-Ray Observatory. IUE observations were conducted over the wavelength range 1200-3200 A (5-10 eV) and are compared with archival UV measurements spanning the period 1988-1991. This set of observations was analyzed with a uniform, standardized data-reduction procedure. No significant variability in the UV spectrum of 3C 279 is noted over timescales of hours, though variations at the 3 sigma level or higher exist on longer timescales of months to years. The UV observations which most closely bracket the gamma-ray flare detected by EGRET show approximately 3 sigma differences in flux and spectral index, consistent with (but not definitive proof of) variations in the UV flux period of the gamma-ray flare. Statistically marginal evidence for a monotonic correlation is found between UV spectral index and the emission observed from 3C 279, in that a harder spectrum is associated with increased UV flux.

Bonnell, Jerry T.↗
NASA NTRS1999

Observations of Gamma-Ray Bursts

Gamma-ray bursts are now generally believed to originate from cosmological distances and represent the largest known explosions in the Universe. These lectures will describe the temporal and spectral characteristic of gamma-ray bursts, their intensity and sky distribution, and other observed characteristics in the gamma-ray region, primarily from data obtained with the BATSE experiment on the Compton Observatory. A summary of recent discoveries and observations in other wavelength regions will also be presented, along with their implications for models of the burst emission mechanism. Various possibilities and models for the energy source(s) of gamma-ray bursts will be described.

Fishman, Gerald J.↗
NASA NTRS1998

Use of a Passive Reaction Wheel Jitter Isolation System to Meet the Advanced X-Ray Astrophysics Facility Imaging Performance Requirements

Third in the series of NASA great observatories, the Advanced X-Ray Astrophysics Facility (AXAF) is scheduled for launch from the Space Shuttle in November of 1998. Following in the path of the Hubble Space Telescope and the Compton Gamma Ray Observatory, this observatory will image light at X-ray wavelengths, facilitating the detailed study of such phenomena as supernovae and quasars. The AXAF project is sponsored by the Marshall Space Flight Center in Huntsville, Alabama. Because of exacting requirements on the performance of the AXAF optical system, it was necessary to reduce the transmission of reaction wheel jitter disturbances to the observatory. This reduction was accomplished via use of a passive mechanical isolation system to interface the reaction wheels with the spacecraft central structure. In addition to presenting a description of the spacecraft, the isolation system, and the key image quality requirement flowdown, this paper details the analyses performed in support of system-level imaging performance requirement verification. These analyses include the identification of system-level requirement suballocations, quantification of imaging and pointing performance, and formulation of unit-level isolation system transmissibility requirements. Given in comparison to the non-isolated system imaging performance, the results of these analyses clearly illustrate the effectiveness of an innovative reaction wheel passive isolation system.

Pendergast, Karl J.↗
NASA NTRS1998

Jitter Suppression Via Reaction Wheel Passive Isolation for the NASA Advanced X-Ray Astrophysics Facility

Text: Third in the series of NASA great observatories, the Advanced X-ray Astrophysics Facility (AXAF) is scheduled for launch from the Space Shuttle in September 1998. Following in the path of the Hubble Space Telescope and the Compton Gamma Ray Observatory, this telescope will image light at x-ray wavelengths, facilitating the detailed study of such phenomena as supernovae and quasars. The AXAF program is sponsored by the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Due to exacting requirements on the performance of the AXAF optical system, it is necessary to reduce the transmission of reaction wheel jitter disturbances to the observatory. This reduction is accomplished via use of a passive mechanical isolation system which acts as an interface between the reaction wheels and the spacecraft central structure.

Pendergast, Karl J.↗
NASA NTRS1979

Cosmic far-ultraviolet background radiation - Probe of a dense hot intergalactic medium

Line and continuum radiation fluxes have been computed for a wide range of enriched intergalactic medium (IGM) models. Observations of the diffuse extragalactic light at optical and far-ultraviolet wavelengths are found to provide a potentially important probe of a dense hot intergalactic medium. If the diffuse X-ray background is produced by this gas, the models constrain the cosmological density parameter (Omega) to be less than 0.4. The associated Compton distortions of the cosmic blackbody background radiation and the optical depths to distant quasars at X-ray wavelengths are also evaluated.

Sherman, R. D.↗
NASA NTRS1995

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 4: Multiwavelength analysis

Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lacertae object PKS 2155-304. Intensively sampled ultraviolet and soft X-ray light curves showed a clear temporal correlation with the X-rays leading the ultraviolet by 2-3 hr. This lag was found to be significantly different from zero after an exhaustive comparison of four different techniques for measuring temporal correlations. Variations in the ultraviolet trough optical wave bands were also strongly correlated, with no measurable lag down to limiting timescales of approximately less than 1-2 hr. This strong correlation extends to the near-infrared, but the less intensive sampling precludes measurement of any lag beyomnd an upper limit of approximately less than 1 day. These lags and limits of the order of hours are much shorter than most rapid observed single-band variations. Because of the very sparse radio sampling, it was not possible to measure quantitatively the correlation and lag with shorter wavelengths, but the data do suggest that the radio may lag the optical/ultraviolet by approximately 1 week, with longer delays and weaker variations to longer radio wavelengths. The epoch-folding Q(exp 2) statistic was used to test for periodicity, and no evidence for strict or quasi-periodicity was found in any of the light curves. Because they lead the lower frequencies, the soft X-rays (approximately less than 1 keV) cannot arise from synchrotron self-Compton scattering. These results also rule out the accretion disk model, which predicts a measurable lag between ultraviolet/optical wavelength bands and a correlation between hardness and brightness, neither of which were seen. They are consistent with the entire radio through X-ray continuum arising from direct synchrotron emission from a relativistic jet. However, the tapered jet model, in which the X-ray emission is produced closer in, has problems explaining the magnitude of the ultraviolet/X-ray lag, because the X-ray-emitting electrons have very short lifetimes (t(sub 1/2) much less than 1 s). The result that the lag is much smaller than the variability timescale suggests instead that the radiation may be produced in a flattened region such as a shock front.

Edelson, R.↗
NASA NTRS1994

The 1993 multiwavelength campaign on 3C 279: The radio to gamma-ray energy distribution inlow state

Simultaneous observations of 3C 279 at radio, millimeter, near-infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or 'low' state during this period. Comparing the multiwavelength energy distribution to that from 1991 June, when 3C 279 was in its brightest recorded gamma-ray state, we find the following: (1) 3C 279 faded dramatically at all frequencies above 10(exp 14) Hz, while the flux variations at low frequencies (radio to millimeter wavelengths) were minor. (2) The near-infrared-optical-ultraviolet spectral shape was softer (steeper) in the quiescent state, and the X-ray spectra also appear softer, although the spectral indix measured by ROSAT refer to a lower energy band than that measured earlier with Ginga. (3) The ratio of the gamma-ray luminosity to that across all other frequencies decreased from a value of approximately equal to 10 in the flaring state to a value approximately equal to 1 in the quiescent state. These findings imply that the production of gamma-rays is closely related to the optical-ultraviolet continuum, in agreement with models where gamma-rays are produced through inverse Compton (IC) scattering by relativistic electrons emitting the synchrotron continuum. The observed nonlinear relation between the synchrotron and IC requires both a change in the electron spectrum and an associated change in the seed photons.

Maraschi, L.↗
NASA NTRS1998

Correlation Between Radio-Millimeter and Gamma Ray Fluxes from Blazars

Using multifrequency databases, we have plotted radio (5 GHz, 22 GHz, and 37 GHz) and millimeter (90 GHz and 230 GHz) fluxes versus MeV and gamma-ray fluxes of the EGRET blazar sample. Strong correlations have been found between the emissions at the radio-millimeter wavelengths and they-rays. These correlations have been explained in the frame work of Synchrotron Self-Compton (SSC) processes between the radio-millimeter synchrotron emissions and the shock-accelerated electrons in the jets of blazars. Using this SSC model we are able to explain the GeV spectra of the EGRET blazars. The present model will also explain the physics of TeV flares in blazars and the time lag between the TeV and GeV photons from a blazar.

Ghosh, K. K.↗
NASA NTRS1997

Multi-Wavelength Observations of 3C 273 in 1993-1995

We present the results of the multi-wavelength campaigns on 3C 273 in 1993-1995. During the observations in late 1993 this quasar showed an increase of its flux for energies >= 100 MeV from about 2.1 x 10(exp -7) photons/sq cm.s to approximately 5.6 x 10(exp -7) photons/sq cm.s during a radio outburst at 14.5, 22 and 37 GHz. However, no one-to-one correlation of the gamma-ray radiation with any frequency could be found. The photon spectral index of the high energy spectrum changed from GAMMA(sub gamma) = (3.20 +/- 0.54) to GAMMA(sub gamma) = (2.20 +/- 0.22) in the sense that the spectrum flattened when the gamma-ray flux increased. Fits of the three most prominent models (synchrotron self-Comptonization, external inverse Comptonization and the proton initiated cascade model) for the explanation of the high gamma-ray emission of active galactic nuclei were performed to the multi-wavelength spectrum of 3C 273 . All three models are able to represent the basic features of the multi-wavelength spectrum. Although there are some differences the data are still not decisive enough to discriminate between the models.

vonMontigny, C.↗
NASA NTRS1983

Multifrequency observations of the flaring quasar 1156+295

A report is presented on the optically violent variable quasar 1156+295, known also as 4C 29.45 and Ton 599. A large outburst of this quasar was discovered in April 1981 in the course of a program to obtain simultaneous multifrequency spectra of variable quasars. Ultraviolet observations taken with the International Ultraviolet Explorer satellite were coordinated with ground-based observations at radio, infrared, and optical wavelengths. Measurements were made at four epochs starting immediately after the outburst was discovered, when the B-magnitude was 14.0, and at intervals of 4 days, 60 days and 1 year. The luminosity integrated only over observed wavelength bands was approximately 3 x 10 to the 48th ergs/sec on the first epoch of observation. Modeling of the source with a synchrotron self-Compton model suggests that the core of the source has a linear dimension of 0.01 pc, a magnetic field strength in the range 0.1-30 gauss, and a bulk relativistic motion in the quasar rest frame characterized by a Lorentz factor in the range 2-8.

Glassgold, A. E.↗
NASA NTRS2019

Detection of Nonthermal Hard X-Ray Emission from the “Fermi Bubble” in an External Galaxy

We report new Chandra hard X-ray (>2 keV) and Jansky Very Large Array C-band observations of the nuclear super bubble of NGC 3079, an analog of the “Fermi bubble” in our Milky Way. We detect extended hard X-ray emission on the southwest (SW)side of the galactic nucleus with coherent multiwavelength features in radio, Hα, and soft X-ray. The hard X-ray feature has a cone shape with possibly a weak cap, forming a bubble-like structure with a diameter of∼1.1 kpc. A similar extended feature, however, is not detected on the northeast (NE)side, which is brighter in all other wavelengths such as radio, Hα, and soft X-ray. Scattered photons from the nuclear region or other nearby point-like X-ray bright sources, inverse Compton emission from cosmic-ray(CR)electrons via interaction with the cosmic microwave background, or any individually faint stellar X-ray source populations, cannot explain the extended hard X-ray emission on the SW side and the strongly NE/SW asymmetry. A synchrotron emission model, plus a thermal component accounting for the excess at∼1 keV, can well characterize the broadband radio/hard X-ray spectra. The broadband synchrotron spectra do not show any significant cutoff, and even possibly slightly flatten at higher energy. This rule out a loss-limited scenario in the acceleration of the CR electrons in or around this superbubble. As the first detection of kiloparsec-scale extended hard X-ray emission associated with a galactic nuclear superbubble, the spatial and spectral properties of the multiwavelength emissions indicate that the CR leptons responsible for the broadband synchrotron emission from the SW bubble must be accelerated in situ, instead of transported from the nuclear region of the galaxy.

Jiang-Tao Li↗