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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 NTRS1984

Constraints on continuous beam models of the jet in 3C 273

The one-sidedness, 'superluminal' motion, and detailed spectra observed for 3C 273 put significant constraints on continuous beam models for the source of the extended emission in 3C 273 A. The one-sidedness of the extended emission implies that the age of the radio-frequency cloud is probably about 3-5 Myr. The 'superluminal' motion observed with VLBI constrains the bulk Lorentz factor of the jet to be more than about 10. Finally, the observed X-ray emission from the jet provides a method for deciding the question of beam composition: for a given beam power, an electron-positron beam would produce a much higher (beamed) inverse-Compton X-ray flux off extended-jet optical photons than an electron-proton beam would, thus making the observed weak jet X-ray flux a strong indicator of a proton positive component to the jet. Remaining experimental uncertainties in the case of 3C 273 make it impossible to decide the question of beam composition at present, but the next generation of experiments may make this possible for 3C 273 and other 'superluminal' objects. The above arguments have the advantage of not depending on the details of the mechanism for producing the high-energy radio-cloud electrons.

Roberts, D.↗
NASA NTRS1981

Compact radio source 1413 + 135 is a far-IR extragalactic object

The radio source 1413 + 135 is shown to be one of the strongest known emitters of millimeter radiation. The energy distribution of this object, measured between meter and X-ray wavelengths, reveals that most of the power emitted by this object comes out at millimeter and far-IR wavelengths. If the emission at 1 mm is due to incoherent synchrotron radiation, then the source must be very compact, with a size around 25 micron arc sec, and contain a magnetic field larger than 10 G. The steep spectral index in the near-IR is attributed to a high-energy cutoff in the distribution of synchrotron emitting electrons at a Lorentz factor of approximately 300.

Beichman, C. A.↗
NASA NTRS1983

The soft X-ray background

Soft-X-ray maps in the B, C, and M (130-188, 160-284, and 440-1100-eV) bands, based on sounding-rocket observations obtained in the Wisconsin all-sky survey over a 10-yr period are presented and discussed. The B and C band maps are found to be similar, and comparison with the H I column densities of Cleary et al. (1979) shows an anticorrelation of B and C emission with neutral gas, implying hot-interstellar-gas emission from within 100 pc of the sun. The M-band pattern is different, and may be due to extragalactic high-energy diffuse emission and/or M dwarfs, although extragalactic sources are not specifically required to explain the data.

Kraushaar, W.↗
NASA NTRS1981

On ionization equilibrium in solar flares as determined from X-ray emissionlines of Ca XVIII and Ca XIX

A diagnostic capable of determining the state of ionization equilibrium in flare plasmas is important for the determination of the physical conditions in flares. An experiment on the Air Force satellite P78-1 has provided high-resolution X-ray spectra which make it possible to determine the state of the ionization equilibrium in coronal flare plasmas. The considered investigation has the objective to show that the interpretation of the calcium results is complicated by several possible blends to line q, and to point out a variation in the observed ratios which seems difficult to account for. Possible explanations for the observations are discussed, taking into account the possibility that the ionization equilibrium calculations have to be improved. Another possible explanation is related to a suggestion made by Urnov (1981) and Karev et al. (1980) concerning the effects produced by the presence of high-energy nonthermal electrons.

Doscher, G. A.↗
NASA NTRS1977

Recent high energy gamma-ray results from SAS-2

Recent developments in gamma-ray astronomy due to the results from SAS-2 have focused on two areas. First, the emission from the plane of the Galaxy is the dominant feature in the gamma-ray sky. The galactic latitude and longitude distributions are consistent with the concept that the high-energy radiation originates from cosmic rays interacting with interstellar matter, and the measurements support a galactic origin for cosmic rays. Second, searches of the SAS-2 data for emission from localized sources have shown three strong discrete gamma-ray sources: the Crab nebula and PSR 0531 + 21, the Vela supernova remnant and PSR 0833-45, and a source near galactic coordinates 193 deg longitude, +3 deg latitude, which does not appear to be associated with other known celestial objects. Evidence has also been found for pulsed gamma-ray emission from two other radio pulsars, PSR 1818-04 and PSR 1747-46. A localized source near longitudes 76-80 deg may be associated with the X-ray source Cyg X-3.

Thompson, D. J.↗
NASA NTRS1977

Very high-energy gamma ray astronomy

Recent results in ground-based very high-energy (less than 10 to the eleventh power eV) gamma-ray astronomy are reviewed. The various modes of the atmospheric Cerenkov technique are described, and the importance of cosmic ray rejection methods is stressed. The positive detections (at approximately less than 10 to the 12th power eV) of the Crab pulsar that suggest a very flat spectrum and time-variable pulse phase are discussed. Observations of other pulsars (particularly Vela) suggest that these features may be general. The steady flux upper limits for the Crab Nebula are thus reconsidered, and a new value of the implied (Compton-synchrotron) magnetic field in the Nebula is reported. Evidence that a 4.8-hour modulated effect was detected at E sub gamma is less than 10 to the 12th power eV from Cyg X-3 is strengthened in that the exact period originally proposed agrees well with a recent determination of the X-ray period. The southern sky observations are reviewed, and the significance of the detection of an active galaxy (NGC 5128) is considered for source models and future observations.

Grindlay, J. E.↗
NASA NTRS1977

A hard X-ray imaging instrument for solar and cosmic sources

A hard X-ray imaging instrument is described which is capable of high-resolution imaging of solar and cosmic hard X-ray sources between 2 and 80 keV during Shuttle sortie flights. The properties of solar burst sources and the resulting instrument requirements are discussed. The instrument envelope of 1.2 x 1.2 x 3.0 meters includes a tungsten multigrid collimator which has 4-arcsec resolution, a 40-arcmin response envelope and a point-source effective area of 26 sq cm. A combination of periodic fan beams and nonperiodic pencil beams enables a unique deconvolution to be achieved within a 128 x 128 arcsec field without mechanical scanning. The detector system is a set of direct-readout 40 atm-cm xenon-filled proportional counters designed to minimize background. The instrument is capable of refurbishment to optimize the collimator configuration for specific solar or cosmic scientific objectives, to upgrade the angular resolution, or to extend the high-energy response.

Hurford, G. J.↗
NASA NTRS1974

Search for brief celestial X-ray bursts

The occurrence of intense bursts of 0.1- to 1.5-MeV photons from space has been confirmed with observations from IMP-6. This is the first positive result of an extensive data comparison, in which a search was made of OGO and IMP records for time coincidences between brief X- or gamma-ray increases and a variety of other transient phenomena. The IMP-6 measurements provided the first differential energy spectra of these events, the shapes of which indicate that photons predominantly in the gamma-ray domain are released into space. Whether these bursts originate in distant supernovae or in some new class of relatively nearby gamma-ray flare stars, they reveal a process which is new to high-energy astrophysics, not only because of the unusual spectrum, but also because of the brief time scales involved and because of the intense fluxes observed.

Cline, T. L.↗
NASA NTRS1974

Correlation analysis of X-ray emission from Cygnus X-1

Normalized autocorrelation and cross-correlation coefficients have been calculated for the X-ray emission of Cygnus X-1 in two energy bins, 2.1-5.1 keV and 5.1-12 keV. The analysis shows a strong correlation between the pulsations in the two energy bins, with the low-energy pulsations lagging behind the high-energy ones, or alternatively a shorter duration of the pulse trains in the high-energy bin. The power spectral density derived from the autocorrelation functions indicates a larger contribution of the high-frequency components for the higher-energy X-rays.

Brinkman, A. C.↗
NASA NTRS1977

Interpretation of the silver L X-ray spectrum

Analysis of the Ag L-series X-ray spectrum has been performed, based on relaxed-orbital relativistic transition-energy calculations. Satellite energies were computed in intermediate coupling. It is found that satellites arising from LN double-hole states generally fall within the natural width of the parent diagram lines. Contrary to previous assumption, the observed high-energy satellites are due to LM double-hole states produced by L1-L3M4,5 Coster-Kronig transitions and by shakeoff. The observed peak structure in the satellite spectrum is due to multiplet splitting of the initial and final double-hole states. Theoretical L1-L3M4,5 transition rates based on the Coster-Kronig energies computed by Chen et al. (1977) are closer to experiment than previous results, but still are too large by a factor of about 2, indicating an as-yet undetected flaw in the theory.

Chen, M. H.↗
NASA NTRS1978

High-energy proton radiation damage of high-purity germanium detectors

Quantitative studies of radiation damage in high-purity germanium gamma-ray detectors due to high-energy charged particles have been carried out; two 1.0 cm thick planar detectors were irradiated by 6 GeV/c protons. Under proton bombardment, degradation in the energy resolution was found to begin below 7 x 10 to the 7th protons/sq cm and increased proportionately in both detectors until the experiment was terminated at a total flux of 5.7 x 10 to the 8th protons/sq cm, equivalent to about a six year exposure to cosmic-ray protons in space. At the end of the irradiation, the FWHM resolution measured at 1332 keV stood at 8.5 and 13.6 keV, with both detectors of only marginal utility as a spectrometer due to the severe tailing caused by charge trapping. Annealing these detectors after proton damage was found to be much easier than after neutron damage.

Pehl, R. H.↗
NASA NTRS1979

High energy X-ray observations of Sco-like sources with Ariel V

Results are reported for observations of Sco X-1 and the similar sources 4U 1702-36 (GX 349+2, Sco X-2), 4U 1813-14 (GX 17+2), and 4U 1758-25 (GX 5-1) by several of the X-ray telescopes aboard the Ariel 5 satellite over the energy range from 2 to approximately 100 keV. The results confirm the existence of a high-energy tail in the spectrum of Sco X-1, demonstrate that 4U 1702-36 has a similar spectrum, and provide evidence for a variation of the 26-56-keV flux from 4U 1702-36 by more than a factor of four with no related change in the 2.9-7.6-keV flux. The high-energy emission from Sco X-1 is found to be one to two orders of magnitude above the extrapolated low-energy emission. Observed X-ray, radio, and optical properties of these four sources, as well as two additional Sco-like sources, are summarized.

Greenhill, J. G.↗
NASA NTRS1979

Detector arrays for photometric measurements at soft X-ray, ultraviolet and visible wavelengths

The construction and modes of operation of the Multi-Anode Microchannel Array (MAMA) detectors are described, and the designs of spectrometers utilizing them are outlined. MAMA consists of a curved microchannel array plate, an opaque photocathode (peak quantum efficiency of 19% at 1216 A), and a multi-anode (either discrete- or coincidence-anode) readout array. Designed for use in instruments on spaceborne telescopes, MAMA can be operated in a windowless configuration in extreme-ultraviolet and soft X-ray wavelengths, or in a sealed configuration at UV and visible wavelengths. Advantages of MAMA include low applied potential (less than 3.0 kV), high gain (greater than 10 to the 6th electrons/pulse), low sensitivity to high-energy charged particles, and immunity to external magnetic fields of less than 500 Gauss

Timothy, J. G.↗
NASA NTRS1983

Nuclear Science Symposium, 29th, and Symposium on Nuclear Power, 14th, Washington, DC, October 20-22, 1982, Proceedings

High-energy radiation detectors suitable for balloon-borne or space-based radiation event studies are described. The employment of NaI(Tl) scintillator bars for gamma ray detection is outlined, and the development of a fluorescent gated gas-filled scintillation proportional counter is reported. A high throughput nondispersive hard X ray spectrograph with angular resolution for cosmic bursts, transients, and sources has been constructed. Features of a sealed high pressure xenon filled imaging proportional counter with a 30 sq cm sensitive area are explored. Finally, the various radiation effects on electronic circuitry in a space environment are defined, and an MOS dosimeter for assaying the cumulative radiation flux in a spacecraft due to ambient conditions is characterized.

Davis, W. D.↗
NASA NTRS1985

Intensities of high-energy cosmic rays at Mount Kanbala

The energy spectra of atmospheric cosmic rays at Mt. Kanbala (520 g/sq cm.) are measured with emulsion chambers. The power indexes of the spectra are values of about 2.0 for both gamma-rays and hadrons. Those fluxes are consistent with the ones expected from the model of primary cosmic rays with heavy nuclei of high content in the energy around 10 to the 15th power eV.

Ren, J. R.↗
NASA NTRS1985

Intensities of high-energy cosmic rays at Mount Kanbala

General features of family events with Summary E sub gamma 200 TeV, observed by the emulsion chambers at Mt. Kanbala, are presented in comparison with the Monte Carlo simulation. The lateral and cluster structure, and the energy spectra of constituent gamma-rays and hadrons are shown to be consistent with the Monte Carlo results calculated under the assumption of heavy-enriched primary, scaling, QCD jets and increasing cross-section.

Ren, J. R.↗
NASA NTRS1983

Hot accretion disks in the centers of quasars

Hot accretion disks around massive, rotating black holes could exist in the centers of quasars. These hot accretion disks produce copious amounts of e(+)e(-) pairs, gamma-rays and X-rays. Most of the disk models that produce significant amounts of gamma-rays, say 10 percent of the total luminosity, and have an energy flux spectral index at X-rays of order unity, are optically thick to gamma-gamma pair production. Gamma-rays, therefore, more energetic than a few MeV do not escape from the disk but are degraded to lower energy radiation. The application of this picture to specific high-energy spectra of active galactic nuclei and quasars as well as high-energy background is explored. A hot accretion disk around a stellar black hole may also account for the positron source in the center of the Milky Way.

Kafatos, M.↗
NASA NTRS1985

High-energy emission in gamma-ray bursts

Between February 1980 and August 1983 the Gamma-Ray Spectrometer on the Solar Maximum Mission Satellite (SMM) detected 72 events identified as being of cosmic origin. These events are an essentially unbiased subset of all gamma-ray bursts. The measured spectra of these events show that high energy (greater than 1 MeV) emission is a common and energetically important feature. There is no evidence for a general high-energy cut-off or a distribution of cut-offs below about 6 MeV. These observations imply a limit on the preferential beaming of high energy emission. This constraint, combined with the assumption of isotropic low energy emission, implies that the typical magnetic field strength at burst radiation sites is less than 1 x 10 to the 12th gauss.

Matz, S. M.↗