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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 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 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

Radio and X-ray observations of NGC 1851 and NGC 1904

The globular clusters NGC 1851 and NGC 1904, have been observed simultaneously at radio and X-ray wavelengths with the aid of the Green Bank interferometer and the proportional counter on OAO Copernicus. The combined radio and X-ray observations provided simultaneous coverage of each subject for a total of about one hour. Data concerning the radio frequency observations of the two globular clusters are presented in a table. The X-ray counts per frame are shown in a graph as a function of time, taking into account a five day interval in December 1975.

Johnson, H. M.↗
NASA NTRS2004

G65.2+5.7: A Thermal Composite Supernova Remnant with a Cool Shell

This paper presents archival ROSAT PSPC observations of the G65.2+5.7 supernova remnant (also known as G65.3+5.7). Little material obscures this remnant and so it was well observed, even at the softest end of ROSATs bandpass (approx. 0.11 to 0.28 keV). These soft X-ray images reveal the remnant s centrally-filled morphology which, in combination with existing radio frequency observations, places G65.2+5.7 in the thermal composite (mixed morphology) class of supernova remnants. Not only might G65.2+5.7 be the oldest known thermal composite supernova remnant, but owing to its optically revealed cool, dense shell, this remnant supports the proposal that thermal composite supernova remnants lack X-ray bright shells because they have evolved beyond the adiabatic phase. These observations also reveal a slightly extended point source centered on RA = l9(sup h) 36(sup m) 46(sup s). dec = 30 deg.40 min.07 sec.and extending 6.5 arc min in radius in the band 67 map. The source of this emission has yet to be discovered, as there is no known pulsar at this location.

Shelton, R. L.↗
NASA NTRS2004

The Hard X-Ray and Coordinated Multifrequency Properties of the Blazar 3C279

Upon our successful AO-1 proposal no. 120085, the quasar 3C 279 has been observed in a coordinated multiwavelength campaign, including INTEGRAL, Chandra, and ground-based radio, near-infrared, and optical observations in June 2003. INTEGRAL observed 3C279 continuously for 300 ksec in INTEGRAL AO-1 between June 1 and June 5,2003. In addition, a Chandra pointing of 5 ksec was done on June 2, the Metsiihovi radio telescope contributed high-frequency radio observations, the SEST observed the source at mm wavelengths, and the 80 cm Turola telescope at La Palma and the 2.3 m telescope at Siding Springs, Australia contributed optical observations.

Collmar, W.↗
NASA NTRS2019

The NANOGrav 11 yr Data Set: Solar Wind Sounding through Pulsar Timing

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has observed dozens ofmillisecond pulsars for over a decade. We have accrued a large collection of dispersion measure (DM)measurements sensitive to the total electron content between Earth and the pulsars at each observation. All lines ofsight cross through the solar wind (SW), which produces correlated DM fluctuations in all pulsars. We develop andapply techniques for extracting the imprint of the SW from the full collection of DM measurements in the recentlyreleased NANOGrav 11 yr data set. We filter out long-timescale DM fluctuations attributable to structure in theinterstellar medium and carry out a simultaneous analysis of all pulsars in our sample that can differentiate thecorrelated signature of the wind from signals unique to individual lines of sight. When treating the SW asspherically symmetric and constant in time, we find the electron number density at 1au to be 7.9 ± 0.2 cm(exp -3). Wefind our data to be insensitive to long-term variation in the density of the wind. We argue that our techniques pairedwith a high-cadence, low-radio-frequency observing campaign of near-ecliptic pulsars would be capable ofmapping out large-scale latitudinal structure in the wind.

Madison, D.R.↗
NASA NTRS1966

Low-frequency radio astronomy

Rockets and satellites used for low frequency radio observations to study cosmic background noise and radio bursts from sun and planets

SOLAR RADIO BURST↗
NASA NTRS1971

Ultraviolet investigations of cosmic X-ray sources and analogous objects

Data on the UV spectrum of the Crab nebula and on UV and radio frequency observations of Wolf-Rayet stars was analyzed. A description of TT Arietis is given. It is concluded that this object must be a double star, since it does not radiate like an ordinary photosphere or a single blackbody. Details of the spectrum are given.

Johnson, H. M.↗
NASA NTRS1975

An anomaly in the flux of Cassiopeia A at 38 MHz

The secular decrease in the flux of the supernova remnant Cassiopeia A has been measured at many radio frequencies. Observations are reported which indicate that this flux decrease has halted at 38 MHz and that the flux is increasing at this frequency. This may indicate that a new era of activity has begun in this object.

Erickson, W. C.↗
NASA NTRS1980

Association of flaring X-ray bright points with type III bursts

Using the swept-frequency radio observations obtained at the Clark Lake Radio Observatory and the X-ray photographs taken by the S-054 experiment aboard Skylab, a search has been made for type III bursts associated with X-ray bright point (XBP) flares. Using temporal as well as spatial criteria for the association, four such events are found over a period of 43 days. The time period was selected in such a way that the level of flare and radio activity was low in order to minimize the chance coincidences. The detection of type III bursts from the flaring XBPs is of great interest, since it identifies them with the flare process, of which XBP flares are thought to be the simplest form.

Kundu, M. R.↗
NASA NTRS1981

CCD photometry of the BL Lacertae objects 1218+304, 1219+28, and 1727+50 - Point sources, associated nebulosity, and broad-band spectra

Visual and far-red surface photometry has been obtained for the X-ray emitting BL Lacertae objects 1218+304 and 1727+50, and the highly variable object 1219+28. The intensity distribution for 1727+50 can be modeled by means of a central point source and a de Vaucouleurs intensity law for an underlying galaxy. The spectral index of the point source of 1727+50 is found to be 0.97, while the indices for 1218+304 and 1219+28 are 0.91 and 1.7, respectively. Comparison of the results presented with X-ray and radio-frequency observations suggests that all emission from 1727+50 and 1218+304 is due to direct synchrotron emission. If this is the case, the relativistic motion effects and continuous particle injection are also implied by the data.

Weistrop, D.↗
NASA NTRS2012

The Radio Light Curve of the Gamma-Ray Nova in V407 CYG: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast

We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array (VLA) and spanning 1.45 GHz and 17.770 days following discovery. This nova.the first ever detected in gamma rays.shows a radio light curve dominated by the wind of the Mira giant companion, rather than the nova ejecta themselves. The radio luminosity grewas the wind became increasingly ionized by the nova outburst, and faded as the wind was violently heated from within by the nova shock. This study marks the first time that this physical mechanism has been shown to dominate the radio light curve of an astrophysical transient. We do not observe a thermal signature from the nova ejecta or synchrotron emission from the shock, due to the fact that these components were hidden behind the absorbing screen of the Mira wind. We estimate a mass-loss rate for the Mira wind of .Mw approximately equals 10(exp -6) Solar mass yr(exp -1). We also present the only radio detection of V407 Cyg before the 2010 nova, gleaned from unpublished 1993 archival VLA data, which shows that the radio luminosity of the Mira wind varies by a factor of 20 even in quiescence. Although V407 Cyg likely hosts a massive accreting white dwarf, making it a candidate progenitor system for a Type Ia supernova, the dense and radially continuous circumbinary material surrounding V407 Cyg is inconsistent with observational constraints on the environments of most Type Ia supernovae.

Chomiuk, Laura↗
NASA NTRS1991

New observations of the low frequency interplanetary radio emissions

Recent Voyager 1 observations reveal reoccurrences of the low frequency interplanetary radio emissions. Three of the new events are weak transient events which rise in frequency from the range of 2-2.5 kHz to about 3 kHz with drift rates of about 1.5 kHz/year. The first of the transient events begins in mid-1989 and the more recent pair of events was first detected in late 1990. In addition, there is an apparent onset of a 2-kHz component of the emission beginning near day 70 of 1991. The new transient emissions are barely detectable on Voyager 1 and are below the threshold of detectability on Voyager 2. The new activity provides new opportunities to test various theories of the triggering, generation, and propagation of the outer heliospheric radio emissions and may signal a response of the source of the radio emissions to the increased solar activity associated with the recent peak in the solar cycle.

Kurth, W. S.↗
NASA NTRS1991

New observations of the low frequency interplanetary radio emissions

Recent Voyager 1 observations reveal reoccurrences of the low frequency interplanetary radio emissions. Three of the new events are weak transient events which rise in frequency from the range of 2-2.5 kHz to about 3 kHz with drift rates of approximately 1.5 kHz/year. The first of the transient events begins in mid-1989 and the more recent pair of events both were first detected in late 1991. In addition, there is an apparent onset of a 2-kHz component of the emission beginning near day 70 of 1991. The new transient emissions are barely detectable on Voyager 1 and are below the threshold of detectability on Voyager 2, which is less sensitive than Voyager 1. The new activity provides new opportunities to test various theories of the triggering, generation, and propagation of the outer heliospheric radio emissions and may signal a response of the source of the radio emissions to the increased solar activity associated with the recent peak in the solar cycle.

Kurth, W. S.↗
NASA NTRS1979

Latitudinal beaming of Jupiter's low frequency radio emissions

Observations of Jupiter's radio emissions from Jovigraphic latitudes greater than 3.3 deg are reported. The measurements were obtained from the Voyager 2 spacecraft at declinations up to 6.5 deg, and when these results are compared with simultaneous observations from Voyager 1 near the ecliptic plane (at a Jovigraphic latitude of about 3 deg), they indicate that the latitudinal-beaming effects persist and may even become stronger with higher latitudes. The results were combined with earlier low-frequency measurements from periods with De as low as -3 deg in order to show the beaming effects the occurrence of the emission over a full 10 deg range of altitude. The results of observations at frequencies near 1 MHz are also discussed, which were obtained from Voyager 1 and 2 in 1978, Rae 1 in 1969, and Imp 6 in 1971-1972. The implications of the new results for models of Jupiter's radio-emission beam pattern are considered.

Alexander, J. K.↗
NASA NTRS1992

Low Frequency Interstellar Scattering and Pulsar Observations

Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

Cordes, James M.↗
NASA NTRS1973

Satellite observations of type 3 solar radio bursts at low frequencies

Type III solar radio bursts were observed from 10 MHz to 10 KHz by satellite experiments above the terrestrial plasmasphere. Solar radio emission in this frequency range results from excitation of the interplanetary plasma by energetic particles propagating outward along open field lines over distances from 5 solar radii to at least 1 AU from the sun. This review summarizes the morphology, characteristics and analysis of individual as well as storms of bursts. Burst rise times are interpreted in terms of exciter length and dispersion while decay times refer to the radiation damping process. The combination of radio observations at the lower frequencies and in-situ measurements on nonrelativistic electrons at 1 AU provide data on the energy range and efficiency of the wave-particle interactions responsible for the radio emission.

Fainberg, J.↗