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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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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

TAROGE-M: radio antenna array on antarctic high mountain for detecting near-horizontal ultra-high energy air showers

The TAROGE-M radio observatory is a self-triggered antenna array on top of the ∼2700 m high Mt. Melbourne in Antarctica, designed to detect impulsive geomagnetic emission from extensive air showers induced by ultra-high energy (UHE) particles beyond 1017 eV, including cosmic rays, Earth-skimming tau neutrinos, and particularly, the “ANITA anomalous events” (AAE) from near and below the horizon. The six AAE discovered by the ANITA experiment have signal features similar to tau neutrinos but that hypothesis is in tension either with the interaction length predicted by Standard Model or with the flux limits set by other experiments. Their origin remains uncertain, requiring more experimental inputs for clarification.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Interstellar O2. I - Abundance, excitation, and prospects for detection of O-16O-18 at radio frequencies

Molecular oxygen, O2, is predicted to be an important constituent of the interstellar gas, but it has not yet been detected in interstellar clouds. In this paper, the gas phase production and destruction of O2 are reconsidered, a non-LTE calculation of level populations at cloud temperatures is presented, and O2 column densities in diffuse and dark clouds are predicted. Ground-based detection of the 234 GHz line of O-16O-18 is shown to be feasible; if CO and O2 are comparable in abundance in clouds similar to the Taurus molecular cloud or in giant molecular clouds, the brightness temperature is predicted to be 0.1 K.

Black, J. H.↗
NASA NTRS2018

Bow Shock in Merging Cluster A520: The Edge of the Radio Halo and the Electron-Proton Equilibration Timescale

We studied the prominent bow shock in the merging galaxy cluster A520 using a deep Chandra X-ray observation and archival VLA radio data. This shock is a useful diagnostic tool, owing to its clear geometry and relatively high Mach number. At the "nose" of the shock, we measure a Mach number of M=2.4(sup 0.4, sub -0.2). The shock becomes oblique away from the merger axis, with the Mach number falling to approx. 1.6 around 30 deg from the nose. The electron temperature immediately behind the shock nose is consistent with that from the Rankine-Hugoniot adiabat, and is higher (at a 95% confidence) than expected for adiabatic compression of electrons followed by Coulomb electron-proton equilibration, indicating the presence of equilibration mechanisms faster than Coulomb collisions. This is similar to an earlier finding for the Bullet cluster. We also combined four archival VLA data sets to obtain a better image of the cluster's giant radio halo at 1.4 GHz. An abrupt edge of the radio halo traces the shock front, and no emission is detected in the pre-shock region. If the radio edge were due only to adiabatic compression of relativistic electrons in pre-shock plasma, we would expect a pre-shock radio emission detectable in this radio data set; however, an interferometric artifact dominates the uncertainty, so we cannot rule this model out. Other interesting features of the radio halo include a peak at the remnant of the cool core, suggesting that the core used to have a radio minihalo, and a peak marking a possible region of high turbulence.

Wang, Qian H. S.↗
DOE OSTI2022

The WISE-2MASS Survey: Red Quasars Into the Radio Quiet Regime

We present a highly complete sample of broad-line (Type 1) QSOs out to z ~ 3 selected by their mid-infrared colors, a method that is minimally affected by dust reddening. We remove host-galaxy emission from the spectra and fit for excess reddening in the residual QSOs, resulting in a Gaussian distribution of colors for unreddened (blue) QSOs, with a tail extending toward heavily reddened (red) QSOs, defined as having E(B – V) > 0.25. This radio-independent selection method enables us to compare red and blue QSO radio properties in both the FIRST (1.4 GHz) and VLASS (2–4 GHz) surveys. Consistent with recent results from optically selected QSOs from SDSS, we find that red QSOs have a significantly higher detection fraction and a higher fraction of compact radio morphologies at both frequencies. We employ radio stacking to investigate the median radio properties of the QSOs including those that are undetected in FIRST and VLASS, finding that red QSOs have significantly brighter radio emission and steeper radio spectral slopes compared with blue QSOs. Finally, we find that the incidence of red QSOs is strongly luminosity dependent, where red QSOs make up >40% of all QSOs at the highest luminosities. Overall, red QSOs comprise ~40% of higher luminosity QSOs, dropping to only a few percent at lower luminosities. Furthermore, red QSOs make up a larger percentage of the radio-detected QSO population. We argue that dusty AGN-driven winds are responsible for both the obscuration as well as excess radio emission seen in red QSOs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099

The RS CVn system HR 1099 was observed with a five station VLBI array at a frequency of 8.4 GHz during a strong radio outburst of approximately 400 mJy. The data are consistent with a circular Gaussian source of 0.8 + or - 0.12 milli-arcsec (FWHM), corresponding to a linear size of 4 + or - 0.6 x 10 to the 11th cm. This is comparable to the distance between the surfaces of the two stars, or to 75 percent of the diameter of the chromospherically active K star. Extrapolation of published photometric data shows that the starspot formation of HR 1099 was facing toward the observers at the times of observations. The high equivalent brightness temperature, approximately 10 billion K, is consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of strength about 30 gauss.

Mutel, R. L.↗
NASA NTRS1994

A revised analysis of micron-sized particles detected near Saturn by the Voyager 2 plasma wave instrument

The impulsive noise that the plasma wave and radio astronomy instruments detected during the Voyager 2 swing by Saturn was attributed to dust grains striking the spacecraft. This report presents a reanalysis of the dust impacts recorded by the plasma wave instrument using an improved model for the response of the electric antenna to dust impacts. The fundamental assumption used in this analysis is that the voltage induced on the antenna is proportional to the mass of the impacting grain. Using the above assumption and the antenna response constants used at Uranus and Neptune, the following conclusions can be reached. The primary dust distribution consists of a 'disk' of particles that coincides with the equator plane and has a north-south thickness of 2-Delta zeta = 962 km. A less dense 'halo' with a north-south thickness of 2-Delta zeta = 3376 km surrounds the primary distribution. The dust particle sizes are of the order of 10 microns, assuming a mass density of 1 g/cu cm. The corresponding particle masses are of the order of 10(exp -9) g, and maximum number densities are of the order of 10(exp -2)/cu m. Most likely, the G ring is the dominate source since the particles were observed very close to that ring, namely at 2.86 R(sub S). Other sources, like nearby moons, are not ruled out especially when perturbations due to electromagnetic forces are included. The calculated optical depth differs by about a factor of 2 from photometric studies. The current particle masses, radii, and the effective north-south thickness of the particle distribution are larger than what Gurnett et al. (1983) reported by about 2, 1, and 1 orders of magnitude, respectively. This is attributed to the fact that the collection coefficient used in this study is smaller than what was used in Gurnett et al.'s earlier publication.

Tsintikidis, D.↗
NASA NTRS1996

Radio Emissions from the Outer Heliosphere

For nearly fifteen years the Voyager 1 and 2 spacecraft have been detecting an unusual radio emission in the outer heliosphere in the frequency range from about 2 to 3 kHz. Two major events have been observed, the first in 1983-84 and the second in 1992-93. In both cases the onset of the radio emission occurred about 400 days after a period of intense solar activity, the first in mid-July 1982, and the second in May-June 1991. These two periods of solar activity produced the two deepest cosmic ray Forbush decreases ever observed. Forbush decreases are indicative of a system of strong shocks and associated disturbances propagating outward through the heliosphere. The radio emission is believed to have been produced when this system of shocks and disturbances interacted with one of the outer boundaries of the heliosphere, most likely in the vicinity of the the heliopause. The emission is believed to be generated by the shock-driven Langmuir-wave mode conversion mechanism, which produces radiation at the plasma frequency (f(sub p)) and at twice the plasma frequency (2f(sub p)). From the 400-day travel time and the known speed of the shocks, the distance to the interaction region can be computed, and is estimated to be in the range from about 110 to 160 AU.

Gurnett, D. A.↗
NASA NTRS1988

Ground-level detection of low- and medium-frequency auroral radio emissions

Natural radio emissions in the frequency range of several hundred kHz were detected at ground level in the auroral region during a ground-level observing program conducted near Fairbanks, Alaska in the spring of 1986 in an attempt to detect auroral cyclotron-maser-generated whistler modes. Most of the strongest emissions were observed in a small time interval around midnight magnetic local time, suggesting a close tie-in with auroral processes. The results support earlier reports of radio noise from the aurora at frequencies of about 100 kHz and indicate the importance of extending the upper frequency of ground-based high-latitude VLF stations to the vicinity of 1 MHz.

Benson, Robert F.↗
NASA NTRS2021

Microwave Radiometer RFI Detection Using Deep Learning

Radio frequency interference (RFI) is a risk for microwave radiometers due to their requirement of very high sensitivity. The Soil Moisture Active Passive (SMAP) mission has an aggressive approach to RFI detection and filtering using dedicated spaceflight hardware and ground processing software. As more sensors push to observe at larger bandwidths in unprotected or shared spectrum, RFI detection continues to be essential. This article presents a deep learning approach to RFI detection using SMAP spectrogram data as input images. The study utilizes the benefits of transfer learning to evaluate the viability of this method for RFI detection in microwave radiometers. The well-known pretrained convolutional neural networks, AlexNet, GoogleNet, and ResNet-101 were investigated. ResNet-101 provided the highest accuracy with respect to validation data (99%), while AlexNet exhibited the highest agreement with SMAP detection (92%).

Microwave radiometry↗
NASA NTRS1993

The radio counterpart of the Z source GX 340+0

We report the detection of a variable radio source at the position of the low-mass X-ray binary GX 340+0. This detection confirms the expectation that all six Z sources are variable radio sources.

Penninx, W.↗
NASA NTRS1991

X-ray emission from poor clusters of galaxies

The X-ray, optical, and radio properties of a sample of 25 poor clusters of galaxies were investigated on the basis of published observations. The X-ray emission from poor clusters was classified into morphological types depending on whether they contain a dominant galaxy or not, as was done by Jones and Forman (1984) for rich clusters. It was found that 13 of the clusters could be classified as D-type clusters, where the peak coincides with a dominant galaxy. For the five T-type clusters in this group, it was found that radio sources are detected almost three times as often as in D-type clusters, indicating that the production of radio sources in poor clusters may be dependent on the shape of the cluster potential well. The optical properties of seven clusters that were not detected at X-ray wavelengths are indistinguishable from those of the X-ray detected clusters, indicating that all poor clusters have a hot intracluster medium.

Price, Rob↗
NASA NTRS1973

Radio stars and X-ray sources.

Limits on the X-ray emission from the known radio stars that can be studied with Uhuru are of interest because of the possible association between X-ray binaries and radio star binaries, and because limits or measurements of the X-ray fluxes can help determine the source of the radio emission. It is shown that if, for the moment, HDE226868 is ignored, none of the radio stars was detected as an X-ray source. It appears that there are two types of radio binary stars, one which is a strong X-ray source and one which is not.

Bahcall, J. N.↗
NASA NTRS1985

In search of Uranian decametric emission

An experiment to detect decametric radiation from Uranus is described. It is argued that in light of recent discoveries of a magnetic field on Uranus, it may be possible to detect low-frequency radio emission similar to the decametric emission from Jupiter. The experiment consisted of 106 hours of monitoring using the 26.3 MHz array of the University of Florida Dixie County Radio Observatory. No radiation from Uranus was detected. An upper flux density limit of 400 Jy was obtained.

Lebo, G. R.↗
NASA NTRS1991

Restrictions on the characteristics of Neptunian lightning

Although lightning-triggered whistlers were detected by the Voyager 2 plasma wave experiment at Neptune, only four possible lightning sferics were detected by the planetary radio astronomy instrument. This low level of detection places strict limits on the characteristics of Neptunian lightning, ruling out lightning with power levels as high as those observed at Saturn or Uranus, but leaving the intriguing possibility that lightning slightly stronger than normal terrestrial lightning flashes but with much lower occurrence rate could exist. Possible scenarios to explain the observations are examined, including reduced NH3 concentration in the planet's atmosphere and an unusually slow risetime discharge process.

Kaiser, M. L.↗
NASA NTRS1989

Interstellar matter in early-type galaxies. III - Radio emission and star formation

The relationship between the IR and radio luminosity in early-type galaxies is examined using the correlation among spiral galaxies as a diagnostic of the presence of star formation. For ellipticals, the presence of long-wavelength IR emission enhances the probability that the galaxy is a radio source and is also correlated with the strength of that source. These findings are consistent with the idea that active radio nuclei are due to black holes being fueled by accretion of gas. The majority of S0s detected in both radio and far-IR have a similar ratio of IR to radio luminosity as has been found in spirals, and which is considered to be indicative of recent star formation. Sensitive radio limits for several galaxies reveal another substantial population of S0s with moderately strong IR emission unaccompanied by radio power.

Walsh, D. E. P.↗