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All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

BATSE Observations of Gamma-Ray Burst Tails

With the observation of low-energy radiation coming from the site of gamma-ray bursts in the hours to weeks after the initial gamma ray burst, it appears that astronomers have discovered a cosmological imprint made by the burster on its surroundings. This paper discusses the phenomenon of postburst emission in Burst and Transient Source Experiment (BATSE) gamma-ray bursts at energies usually associated with prompt emission. After summing up the background-subtracted signals from hundreds of bursts, it is found that tails out to hundreds of seconds after the trigger could be a common feature of events of a duration greater than 2 seconds, and perhaps of the shorter bursts at a lower and shorter-lived level. The tail component may be softer and seems independent of the duration (within the long-GRB sample) and brightness of the prompt burst emission. Some individual bursts have visible tails at gamma-ray energies, and the spectrum in a few cases differs from that of the prompt emission. For one of these bursts, GRB 991216, afterglow at lower energies was detected, which raised the possibility of seeing afterglow observations over large energy ranges using the next generation of GRB detectors in addition to sensitive space- or ground-based telescopes.

Connaughton, Valerie↗
NASA NTRS2002

Chandra and XMM Observations of the ADC Source 0921-630

We analyze observations of the low mass X-ray binary 2S0921-63 obtained with the gratings and CCDs on Chandra and XMM. This object is a high inclination system showing evidence for an accretion disk corona (ADC). Such a corona has the potential to constrain the properties of the heated accretion disk in this system, and other LMXBs by extension. We find evidence for line emission which is generally consistent with that found by previous experiments, although we are able to detect more lines. For the first time in this source, we find that the iron K line has multiple components. We set limits on the line widths and velocity offsets, and we fit the spectra to photoionization models and discuss the implications for accretion disk corona models. For the first time in any ADC source we use these fits, together with density constraints based on the O VII line ratio, in order to constrain the flux in the medium-ionization region of the ADC. Under various assumptions about the source luminosity this constrains the location of the emitting region. These estimates, together with estimates for the emission measure, favor a scenario in which the intrinsic luminosity of the source is comparable to what we observe.

Kallman, T. R.↗
NASA NTRS1980

Plasmas in Saturn's magnetosphere

The solar wind plasma analyzer on board Pioneer 2 provides first observations of low-energy positive ions in the magnetosphere of Saturn. Measurable intensities of ions within the energy-per-unit charge (E/Q) range 100 eV to 8 keV are present over the planetocentric radial distance range about 4 to 16 R sub S in the dayside magnetosphere. The plasmas are found to be rigidly corotating with the planet out to distances of at least 10 R sub S. At radial distances beyond 10 R sub S, the bulk flows appear to be in the corotation direction but with lesser speeds than those expected from rigid corotation. At radial distances beyond the orbit of Rhea at 8.8 R sub S, the dominant ions are most likely protons and the corresponding typical densities and temperatures are 0.5/cu cm and 1,000,000 K, respectively, with substantial fluctuations. It is concluded that the most likely source of these plasmas in the photodissociation of water frost on the surface of the ring material with subsequent ionization of the products and radially outward diffusion. The presence of this plasma torus is expected to have a large influence on the dynamics of Saturn's magnetosphere since the pressure ratio beta of these plasmas approaches unity at radial distances as close to the planet as 6.5 R sub S. On the basis of these observational evidences it is anticipated that quasi-periodic outward flows of plasma, accompanied with a reconfiguration of the magnetosphere beyond about 6.5 R sub S, will occur in the local night sector in order to relieve the plasma pressure from accretion of plasma from the rings.

Frank, L. A.↗
NASA NTRS1987

Low-frequency magnetic field fluctuations in comet P/Halley's magnetosheath - Giotto observations

The interaction region between comets and the solar wind is characterized by large amplitude, low frequency magnetic field fluctuations, both within the upstream region as well as in the magnetosheath. Magnetosheath observations of the magnetic field experiment onboard Giotto indicate values of delta B/B equal to about O(1). Power spectral peaks appear at frequencies of 10mHz with the spectrum exhibiting a power law dependence with an exponent of the order 2. Radial variation of the fluctuation level does not clearly increase with decreasing distance from the cometary nucleus as observed by the magnetometer onboard Vega-1 and as expected from quasi-linear theory. The entrance into the cometary bow shock is furthermore characterized by an order of magnitude increase of the fluctuation level, both on the in- and outbound pass of Giotto.

Glassmeier, K. H.↗
NASA NTRS2019

Probability Index of Low Stratus and Fog at Dawn using Dual Geostationary Satellite Observations from COMS and FY-2D near the Korean Peninsula

We developed a new remote sensing method for detecting low stratus and fog (LSF) at dawn in terms of probability index (PI) of LSF from simultaneous stereo observations of two geostationary-orbit satellites; the Korean Communication, Ocean, and Meteorological Satellite (COMS; 128.2°E); and the Chinese FengYun satellite (FY-2D; 86.5°E). The algorithm was validated near the Korean Peninsula between the months of April and August from April 2012 to June 2015, by using surface observations at 45 meteorological stations in South Korea. The optical features of LSF were estimated by using satellite retrievals and simulated data from the radiative transfer model. The PI was calculated using the combination of three satellite-observed variables: 1) the reflectance at 0.67 μm (R(0.67)) from COMS, and 2) the FY-2D R(0.67) minus the COMS R(0.67) (△R(0.67)) and (3) the FY-2D-COMS difference in the brightness temperature difference between 3.7 and 11.0 μm (ΔBTD(3.7-11)). The three variables, adopted from the top three probability of detection (POD) scores for their fog detection thresholds: △R(0.67) (0.82) > ΔBTD(3.7-11) (0.73) > R(0.67) (0.70) > BTD(3.7-11) (0.51). The LSF PI for this algorithm was significantly better in the two case studies compared to that using COMS only (i.e., R(0.67) or BTD(3.7-11)), so that this improvement was due to △R(0.67) and ΔBTD(3.7-11). Overall, PI in the LSF spatial distribution has the merits of a high detection rate, a specific probability display, and a low rate of seasonality and variability in detection accuracy. Therefore, PI would be useful for monitoring LSF in near-real-time, and to further its forecast ability, using next-generation satellites.

fog↗
NASA NTRS2011

VLA Ammonia Observations of IRAS 16253-2429: A Very Young and Low Mass Protostellar System

IRAS l6253-2429. the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source as possibly one of the youngest and lowest mass sources in formation yet known.

Wiseman, Jennifer J.↗
NASA NTRS1972

ELF noise bands associated with auroral electron precipitation.

Observation of a new type of ELF noise band that is closely associated with low-energy auroral electron precipitation. These observations have been made at relatively low altitudes (less than 3000 km) with the polar-orbiting satellite Injun 5. The noise bands typically have a center frequency of 100 to 300 Hz and often appear to consist of many nearly monochromatic bursts, typically of a few seconds' duration, superimposed to produce the observed noise band. These ELF noise bands are observed only in a relatively narrow range of latitudes (a few degrees) in the auroral zone and are almost always associated with intense fluxes of precipitating electrons with energies from a few hundred electron volts to several kiloelectron volts. On the dayside of the magnetosphere the region where the ELF noise bands and the associated low-energy electron precipitation are observed has been identified as the polar cusp. In considering the possible explanations of these ELF noise bands, it is noted that the spectral characteristics of this noise are very similar to a type of narrowband electromagnetic noise called 'lion's roar,' which has been observed at much higher altitudes in the magnetosheath with the satellite Ogo 5. It is suggested that the ELF noise bands observed at low altitudes with Injun 5 are caused by lion's roar emissions that have propagated down 'open' magnetic-field lines to low altitudes from the magnetosheath region.

Gurnett, D. A.↗
NASA NTRS2003

Transmission measurement based on STM observation to detect the penetration depth of low-energy heavy ions in botanic samples

The penetration depth of low-energy heavy ions in botanic samples was detected with a new transmission measurement. In the measurement, highly oriented pyrolytic graphite (HOPG) pieces were placed behind the botanic samples with certain thickness. During the irradiation of heavy ions with energy of tens of keV, the energetic particles transmitted from those samples were received by the HOPG pieces. After irradiation, scanning tunneling microscope (STM) was applied to observe protrusion-like damage induced by these transmitted ions on the surface of the HOPG. The statistical average number density of protrusions and the minimum transmission rate of the low-energy heavy ions can be obtained. The detection efficiency of the new method for low-energy heavy ions was about 0.1-1 and the background in the measurement can be reduced to as low as 1.0 x 10(8) protrusions/cm2. With this method, the penetration depth of the energetic particles was detected to be no less than 60 micrometers in kidney bean slices when the slices were irradiated by 100 keVAr+ ion at the fluence of 5 x 10(16) ions/cm2. c2002 Elsevier Science Ltd. All rights reserved.

DNA Damage↗
NASA NTRS1992

Resolution and noise properties of the Goddard High-Resolution Spectrograph

The Goddard High-Resolution Spectrograph (GHRS) observation characteristics and data analysis procedures, including deconvolution, are discussed. Particular attention is given to the detection of weak absorption lines in low-signal-to-noise observations. It is found that observations with the GHRS large aperture provide greater sensitivity for the detection of weak, isolated spectral features than does the small aperture for equal observing times. The noise characteristics are well represented by a Poisson distribution at low signal-to-noise characteristics. It is proposed that GHRS observations should be routinely structured with the use of comb-addition, quarter-substepping, FP-SPLITS, and multiple repeats to enable the proper discrimination against noise events capable of mimicking spectral features.

Gilliland, Ronald L.↗
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 NTRS1967

Satellite studies of the lower atmosphere.

Low atmosphere meteorological observations by satellite, discussing sensing of radiation patterns cloud patterns and earth-atmosphere radiative energy balance

Nordberg, W.↗
NASA NTRS1972

HEOS-A2: Press kit

The characteristics of the HEOS-A2 satellite and its assigned mission are discussed. The spacecraft carries seven experiments to investigate the strength and direction of the magnetic fields encountered, the energy distribution of protons and electrons, the nature of the solar winds, detection of micrometeorites, and low frequency solar observations. The highly elliptical polar orbit required for this mission will have an apogee of 38 earth radii. The lifetime of the satellite is expected to be one year minimum.

Allaway, H. G.↗
NASA NTRS1972

Observed relationships between electric fields and auroral particle precipitation

Simultaneous electric field and plasma observations with the low altitude, polar orbiting satellite Injun (Hawkeye) 5 provided a comprehensive survey of convection electric fields and their association with magnetospheric plasma phenomena. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally anti sunward convection poleward convection equatorward of the electric field reversal location. The electric field reversal is interpreted as the boundary between open and closed magnetic field lines. To investigate the electric field and plasma interrelationships during a polar magnetic substorm, a series of passes obtained prior to and during a substrom is presented. Large, anti sunward convection velocities were detected over the polar cap several tens of minutes before the onset of the expansive phase of the substrom. These convection velocities gradually decreased during the decay phase of the substrom. Measurements of enhanced anti sunward flow over the polar cap region are generally consistent with concepts of the origin of substroms.

Gurnett, D. A.↗