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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Comparison of interplanetary type 2 radio burst observations by ISEE-3, Ulysses, and WIND with applications to space weather prediction

Interplanetary (IP) type 2 radio bursts are produced by IP shocks driven by solar ejecta, presumably involving shock acceleration of electrons that leads to radio emission. These radio bursts, which can be detected remotely by a sensitive spacecraft radio receiver, provide a method of tracking the leading edge of solar ejecta moving outward from the sun. Consequently, observations of these bursts sometimes provide advance warning of one or more days prior to the onset of geomagnetic activity induced by the solar ejecta. A robust lower limit on the fraction of intense geomagnetic storms, that are preceded by IP type 2 bursts, is provided. It is shown that 41 percent of the geomagnetic storms occurring during the interval September 1978 to February 1983 were preceded by type 2 events in this catalog, and reasons why the fraction is not larger are addressed. Differences in the observing capabilities of the International Sun-Earth Explorer (ISEE) 3, Ulysses, and WIND, to explain why each of these similar spacecraft radio investigations provides a different perspective of IP type 2 emissions are reviewed.

MacDowall, R. J.↗
NASA NTRS1987

Radio emission from pre-main-sequence stars in Corona Australis

The central region of the Corona Australis molecular cloud surrounding the stars R and TY CrA has been studied using the VLA at 6 cm. Eleven radio sources are detected including five associated with pre-main-sequence objects. The most striking is associated with the near-IR source IRS 7 and shows a complex structure comprising two strong pointlike sources positioned either side of the deeply embedded IR source and two extended lobes of radio emission. The IRS 7 radio source appears to be similar to that associated with Lynds 1551 IRS 5 but has a considerably larger angular size. The other detected sources include the massive pre-main-sequence star TY CrA, the near-IR sources IRS 1 and IRS 5, and the Herbig-Haro object HH 101. The stars R and T CrA were not detected.

Brown, Alexander↗
DOE OSTI2026

Deliberate Motion Analytics Applied to CUAS Sensor Fusion

The Advanced Reactor Safeguards and Security (ARSS) program in the Department of Energy’s Office of Nuclear Energy (DOE-NE) seeks to identify new technology solutions for safeguards and security challenges associated with domestic deployment of advanced nuclear reactors. Research in the ARSS program is investigating alternative physical protection system (PPS) approaches that leverage new detection technologies. This report shows test results from a new form of artificial intelligence (AI) that is called deliberate motion analytics (DMA) when used to spatially and temporally fuse active radar and passive radio frequency (RF) detection that significantly improves detection of uncrewed aircraft systems (UASs). DMA is designed to filter out false positive alarms yet provide highly reliable intrusion detection at nuclear power plants (NPPs) and advanced small modular reactor (ASMR) perimeters. This form of AI is considered to be an enabling technology for security of the future and supports the ARSS investigation of alternative PPSs.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
NASA NTRS1990

Exobiology and SETI from the lunar farside

Within the Life Sciences Division of NASA, the Exobiology Program seeks to understand the origin, evolution and distribution of life in the universe. There are two feasible methods of searching for life beyond the earth. The first is to return to Mars and systematically explore its surface and subsurface with instrumentation capable of identifying extinct as well as extant life. The second is to search for advanced forms of life in other planetary systems that have developed a technology capable of modifying their environment in ways that make it detectable across the vast interstellar distances. The Exobiology Program is currently pursuing both of these options. If NASA's SETI (search for extraterrestrial intelligence) Microwave Observing Project of the 1990s fails to detect evidence of radio signals generated by an extraterrestrial technology, what might be the next step? The establishment of a permanent lunar base early in the next century may enable the construction of large aperture radio telescopes that can extend both the sensitivity and the frequency range of SETI observations. A lunar base may also provide the opportunity for construction of optical and IR telescopes intended for the direct detection of extrasolar planetary systems.

Tarter, Jill C.↗
NASA NTRS1991

First detection of HDO in the atmosphere of Venus at radio wavelengths - An estimate of the H2O vertical distribution

The 225.9 GHz line of HDO has been detected in absorption in the atmosphere of Venus, with the 30-m IRAM antenna. This measurement gives information regarding the vertical distributions of HDO, and thus H2O, in this planet. The observations are consistent with an H2O vertical distribution strongly depleted by saturation at an altitude of 95 km, and, assuming a D/H enrichment of 120 with respect to the terrestrial value, with a mixing ratio of 3.5 (+ or - 2.0) ppm in the range 65-95 km.

Encrenaz, T.↗
NASA NTRS2011

Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered approx.20 new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -30 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.

Harding, Alice K.↗
DOE OSTI2022

The X-shaped Radio Galaxy J0725+5835 is Associated with an AGN Pair

X-shaped radio galaxies (XRGs) are those that exhibit two pairs of unaligned radio lobes (main radio lobes and wings). One of the promising models for the peculiar morphology is jet reorientation. To clarify this, we conducted a 5 GHz observation with the European VLBI Network (EVN) of XRG J0725+5835, which resembles the archetypal binary active galactic nuclei (AGNs) 0402+379 in radio morphology, but it is larger in angular size. In our observation, two milliarcsecond-scale radio components with nonthermal radio emission are detected. Each of them coincides with an optical counterpart with similar photometric redshift and (optical and infrared) magnitude, corresponding to dual active nuclei. Furthermore, with the improved Very Large Array (VLA) images, we find a bridge between the two radio cores and a jet bending in the region surrounding the companion galaxy. This further supports the interplay between the main and companion galaxies. In addition, we also report the discovery of an arcsecond-scale jet in the companion. Given the projected separation of ~100 kpc between the main and companion galaxies, XRG J0725+5835 is likely associated with a dual jetted-AGN system. In both EVN and VLA observations, we find signatures that the jet is changing its direction, which is likely responsible for the X-shaped morphology. For the origin of jet reorientation, several scenarios are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Very Long Baseline Interferometry observations of 257 extragalactic radio sources in the ecliptic region

Very Long Baseline Interferometry observations of 257 extragalactic radio sources with 10 deg of the ecliptic have been conducted at a frequency of 2.29 GHz. Compact components with flux densities greater than 0.1 Jy and angular sizes smaller than the fringe spacings of 2.5 and 3.2 milliarsec were detected in 144 radio sources. This survey was conducted to find compact radio sources to form a high accuracy reference frame for planetary spacecraft navigation. This stable reference frame may also be useful for long-term studies of planetary dynamics.

Wehrle, A. E.↗
DOE OSTI2022

Star formation and AGN feedback in the local Universe: Combining LOFAR and MaNGA

The effect of active galactic nuclei (AGN) on their host galaxies – in particular their levels of star formation – remains one of the key outstanding questions of galaxy evolution. Successful cosmological models of galaxy evolution require a fraction of energy released by an AGN to be redistributed into the interstellar medium to reproduce the observed stellar mass and luminosity function and to prevent the formation of over-massive galaxies. Observations have confirmed that the radio-AGN population is energetically capable of heating and redistributing gas at all phases, however, direct evidence of AGN enhancing or quenching star formation remains rare. With modern, deep radio surveys and large integral field spectroscopy (IFS) surveys, we can detect fainter synchrotron emission from AGN jets and accurately probe the star-forming properties of galaxies, respectively. Here, in this paper, we combine data from the LOw Frequency ARray Two-meter Sky Survey (LoTSS) with data from one of the largest optical IFS surveys, Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), to probe the star-forming properties of 307 local (z < 0.15) galaxies that host radio-detected AGN (RDAGN). We compare our results to a robust control sample of non-active galaxies that each match the stellar mass, redshift, visual morphology, and inclination of a RDAGN host. We find that RDAGN and control galaxies have broad star-formation rate (SFR) distributions, typically lie below the SFMS, and have negative stellar light-weighted age gradients. These results indicate that AGN selected based on their current activity are not responsible for suppressing their host galaxies’ star formation. Rather, our results support the maintenance mode role that radio AGN are expected to have in the local Universe.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

A 5 GHz VLA survey of the galactic plane

We have used the Very Large Array (VLA) to survey the inner Galaxy (absolute value of b less than 0.4 deg, l = 350-40 deg) at 5 GHz to a limiting sensitivity of between 2.5 and 10 mJy. The survey has resulted in a catalog of 1272 discrete sources (including 100 sources outside the formal survey area) of which we have temtatively identified approximately 450 as ultracompact H II regions and approximately 45 as planetary nebulae. Approximately 30% of the radio sources are detected in the Infrared Astronomy Satellite (IRAS) Point source Catalog. The results confirm a scale height of only 30 pc for ultracompact H II regions. We show that source lists generated from the IRAS Point Source Catalog alone suffer serious selection effects; the combination of the IRAS and radio surveys allows us to produce a much more complete census of the regions of massive star formation in our Galaxy.

Becker, Robert H.↗
NASA NTRS1979

The state of technology in electromagnetic (RF) sensors (for lightning detection)

A brief overview of the radio-frequency sensors which were applied to the detection, isolation, and/or identification of the transient electromagnetic energy (sferics) radiated from one or more lightning discharges in the atmosphere is presented. Radio frequency (RF) characteristics of lightning discharges, general RF sensor (antenna) characteristics, sensors and systems previously used for sferic detection, electromagnetic pulse sensors are discussed. References containing extensive bibliographies concerning lightning are presented.

Shumpert, T. H.↗
NASA NTRS2022

Comparable Bulk Radar Attenuation Characteristics Across Both Martian Polar Layered Deposits

The dust-laden and predominantly water ice south polar layered deposits (SPLD) exhibit unique radar behavior at Shallow Radar (SHARAD) frequencies that is not seen in the NPLD. A vertically extensive scattering phenomenon leads to diffuse echoes that obscure radar stratigraphy within the SPLD, referred to as “fog.” Here, we use 2-D and 3-D SHARAD data to measure the areal extent in which the SPLD basal interface can be identified. We also measure reflected power of SPLD basal reflectors and compare those values to ice thickness, regional geomorphology, and the presence of radar echo scattering, to constrain any influence these factors may have on the propagation of radio waves and detectability of the base. Approximately 33% of the area in which the basal interface is observed in Mars Advanced Radar for Subsurface and Ionosphere Sounding data is also detected in SHARAD data. As expected, basal power shows a negative correlation with ice thickness, but the effects of radar fog are less clear. Areas of “column” radar fog patterns exhibit higher average basal power values than regions without radar fog, and areas with only near-surface radar fog have the lowest average basal power values. Our study results suggest that these diffuse echoes may not be associated with radio wave attenuation. Average loss tangent for the SPLD (0.0019 ± 0.0012) indicates no distinguishable difference from previously reported NPLD values in terms of bulk loss properties. We speculate that the SPLD's infrequent reflections compared to the NPLD may be due to the former's dust being less densely packed together to facilitate radar detection.

N Abu Hashmeh↗
DOE OSTI2022

Evidence for X-Ray Emission in Excess to the Jet-afterglow Decay 3.5 yr after the Binary Neutron Star Merger GW 170817: A New Emission Component

For the first ~3 yrs after the binary neutron star merger event GW 170817, the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n < 0.01 cm -3 . We report on observational evidence for an excess of X-ray emission at δt > 900 days after the merger. With L x ≈ 5 × 10 38 erg s -1 at 1234 days, the recently detected X-ray emission represents a ≥ 3.2σ (Gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow at earlier times. In the context of JetFit afterglow models, current data represent a departure with statistical significance ≥ 3.1σ, depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥ 3.7σ. A lack of detectable 3 GHz radio emission suggests a harder broadband spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. In this context, we present a set of ab initio numerical relativity binary neutron star (BNS) merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2011

Improving the Automatic Inversion of Digital ISIS-2 Ionogram Reflection Traces into Topside Vertical Electron-Density Profiles

The topside-sounders on the four satellites of the International Satellites for Ionospheric Studies (ISIS) program were designed as analog systems. The resulting ionograms were displayed on 35-mm film for analysis by visual inspection. Each of these satellites, launched between 1962 and 1971, produced data for 10 to 20 years. A number of the original telemetry tapes from this large data set have been converted directly into digital records. Software, known as the TOPside Ionogram Scalar with True-height (TOPIST) algorithm has been produced that enables the automatic inversion of ISIS-2 ionogram reflection traces into topside vertical electron-density profiles Ne(h). More than million digital Alouette/ISIS topside ionograms have been produced and over 300,000 are from ISIS 2. Many of these ISIS-2 ionograms correspond to a passive mode of operation for the detection of natural radio emissions and thus do not contain ionospheric reflection traces. TOPIST, however, is not able to produce Ne(h) profiles from all of the ISIS-2 ionograms with reflection traces because some of them did not contain frequency information. This information was missing due to difficulties encountered during the analog-to-digital conversion process in the detection of the ionogram frame-sync pulse and/or the frequency markers. Of the many digital topside ionograms that TOPIST was able to process, over 200 were found where direct comparisons could be made with Ne(h) profiles that were produced by manual scaling in the early days of the ISIS program. While many of these comparisons indicated excellent agreement (<10% average difference over the entire profile) there were also many cases with large differences (more than a factor of two). Here we will report on two approaches to improve the automatic inversion process: (1) improve the quality of the digital ionogram database by remedying the missing frequency-information problem when possible, and (2) using the above-mentioned comparisons as teaching examples of how to improve the original TOPIST software.

Benson, R. F.↗
NASA NTRS1989

Radio-continuum emission from the ionized stellar winds of warm supergiants

The Very Large Array has been used at an observing wavelength of 6 cm to survey 25 supergiants of spectral types between B2 and F8. Only one of these stars (Beta Ori, or Rigel) has been detected as a radio-continuum source, with an inferred 6 cm luminosity L6 of 7 x 10 to the 16th ergs/sec per Hz. Rigel may also be an X-ray source (and, if it were, would be the only X-ray detected star out of the 12 stars in this sample that were observed by Einstein. An extended source of more than 10 mJy flux density with the same angular dimensions and location as He 1-5, the planetary nebula surrounding the peculiar supergiant FG Sge, and a weak localized source of roughly 0.1-0.2 mJy somewhat offset from the center of the extended radio emission have also been detected. The upper limits to L6 for the F Ib stars are as much as an order of magnitude below the level at which Rigel was detected. If the radio emission from Rigel is interpreted as free-free radiation from its stellar wind, the inferred ionized mass-loss rate is 2.5 x 10 th the 7th solar mass/yr. The most stringent upper limits to the ionized mass-loss rates obtained for the F and A supergiants are not greater than 10 to the -8th solar mass/yr and less than or equal to 10 to the -7th solar mass/yr, respectively.

Drake, S. A.↗