Engineering Papers⌕ Search

Engineering topics

Rose, W. K.

Publications and source records attributed to Rose, W. K..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151

The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.

Beall, J. H.↗
NASA NTRS1980

On the physical environment in the nucleus of Centaurus A /NGC 5128/

A model is proposed for the radio and X-ray variability of the nucleus of Centaurus A in which an adiabatically expanding plasma containing a power-law distribution of relativistic electrons produces the radio flux by synchrotron emission, and the X-ray flux by inverse Compton scattering of an ambient distribution of thermal photons. The variability of Centaurus A is shown to be consistent with the expansion of an initially opaque, hot (1000-10,000 K) plasma which eventually becomes optically thin. Radio flares without corresponding X-ray flares are possible in this model because the plasma density decreases during the expansion, allowing radio radiation previously absorbed or suppressed to be observed. Some consequences of the model for the physical environment in galactic nuclei are discussed.

Beall, J. H.↗
NASA NTRS1978

Radio and X-ray variability of the nucleus of Centaurus A /NGC 5128/

Centaurus A (NGC 5128) has been observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. These observations, together with results reported by other workers, are interpreted in terms of models of the nucleus of this radio galaxy. The radio observations cover the period from 1973 through early 1977. The X-ray observations cover two 10-day intervals, one in July and August (1975) and the other in July and August 1976. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are shown to be consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons. Upper limits obtained with the model indicate that there may be sufficient energy available in the nucleus to form radio lobes with the same total energy as those already present.

Beall, J. H.↗
NASA NTRS1978

Wave production in an ultrarelativistic electron-positron plasma

In this paper we calculate the eigenmodes associated with an ultrarelativistic electron-positron beam traversing a low-energy electron-positron plasma under physical conditions that may exist along open magnetic field lines above pulsar polar caps. We assume that both beam and plasma are cold and charge neutral, and that magnetic field strength and particle density decrease as the cube of (1/R). In the superstrong magnetic fields near the stellar surface where cyclotron frequencies exceed plasma frequencies, electrostatic waves and associated transverse low-frequency waves are driven unstable by the two-stream type particle distribution. At larger distances above the stellar surface the slow beam cyclotron wave is driven unstable. At even greater radial distance (approximately when particle energy density exceeds magnetic energy density) both the Ordinary and Alfven modes become unstable. All of these instabilities can lead to generation of radiation. If the particle distribution as generated at the stellar surface, assumed to consist of two streams, is modified only by plasma effects, then electrostatic and associated transverse waves may only be unstable near the stellar surface. The beam cyclotron mode which is driven by a two-stream or an inverted particle distribution may be stable.

Hardee, P. E.↗
NASA NTRS1977

An interpretation of galactic observations of CNO isotopes

Nuclear network calculations are used to interpret observations of N-15/N-14 and O-17/O-18 abundance ratios in interstellar clouds. Recent observations of the N-15/N-14 abundance ratio in the galactic disk and the galactic center are consistent with the idea that N-15 is produced in intermediate-mass stars by means of the hot CNO tri-cycle. It is suggested that low-mass stars in the glactic center could be responsible for producing the local enhancement of O-17 by low-temperature (below 100 million K) CNO burning.

Cowan, J. J.↗
NASA NTRS1977

Radio and X-ray variability of the nucleus of Centaurus A (NGC 5128)

Centaurus A was observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons.

Beall, J. H.↗
NASA NTRS1977

Production of C-14 and neutrons in red giants

We have examined the effects of mixing various amounts of hydrogen-rich material into the intershell convective region of red giants undergoing helium shell flashes. We find that significant amounts of C-14 can be produced via the N-14(n, p)C-14 reaction. If substantial portions of this intershell region are mixed out into the envelopes of red giants, then C-14 may be detectable in evolved stars. We find a neutron flux many orders of magnitude above the flux required for the classical s-process, and thus an intermediate neutron process (i-process) may operate in evolved red giants. In all cases studied we find substantial enhancements of O-17. These mixing models offer a plausible explanation of the observations of enhanced O-17 in the carbon star IRC 10216. For certain physical conditions we find significant enhancements of N-15 in the intershell region.

Cowan, J. J.↗
NASA NTRS1977

A new measurement of the spin-up rate of SMC X-1

Observations of the X-ray pulsar, SMC X-1, made from an Aerobee rocket and an Apollo spacecraft have been re-analyzed. The rotation periods found have been combined with observations made from Uhuru, SAS-3, and Ariel 5 to obtain a new measurement of the spin-up rate of SMC X-1.

Yentis, D.↗
NASA NTRS1976

A mechanism for the production of pulsar radio radiation

Recent theoretical studies have suggested that avalanches of electron-positron pairs are produced by spark discharges near the magnetic poles of pulsars. This pair production mechanism may result in a double-peaked particle distribution function. We investigate collective effects caused by a high-energy electron-positron beam traversing a low-energy electron-positron plasma for an astrophysically interesting range of physical parameters. The principal result of this paper is to identify transverse unstable waves whose phase propagation may occur at any arbitrary angle (other than zero) with respect to the magnetic field but whose group velocity is along the magnetic field and approximately the speed of light. It is suggested that the observed radio pulses from pulsars may be caused by the focusing of these transverse waves along the open field lines extending from a pulsar's polar cap to the light cylinder.

Hardee, P. E.↗
NASA NTRS1975

Sources of excitation of the interstellar gas and galactic structure

The excitation of the interstellar gas is discussed in the light of recent evidence from gamma-ray, molecular, and 21-cm line observations. Previous studies of the excitation of the interstellar gas have not taken into account the substantial density contrast that exists between spiral arms and interarm regions. We examine the role played by the galactic distribution of three sources of excitation (supernovae, OB stars, and ultraviolet stars) in determining the physical state of the interstellar gas in arm and interarm regions.

Cowan, J. J.↗
NASA NTRS1972

A model for the Centaurus X-3 phenomenon.

Description of a model for Cen X-3 according to which the X-ray emission comes from an atmosphere heated by shock waves produced by surface pulsations of a white dwarf. This model can explain the luminosity, period, and spectrum of Cen X-3. The way in which these quantities vary with pulsation period and amplitude is discussed.

Blumenthal, G. R.↗