SEARCH · Engineering Papers

Results for “Transient sources”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Location of the gamma-ray transient event of 1979 March 5

The paper discusses the gamma event of Mar. 5, 1979, the most intense burst of nonsolar high-energy photons ever recorded, which was observed by 12 gamma burst instruments on nine spacecraft. The fast rise time of the event and ephemeris and absolute time information from the spacecraft are considered, and a unique and redundantly determined 1 x 2 arcmin error box centered at R.A. = 5h 25.95m, decl. = -66 deg 07.1 arcmin (equinox 1950.0) is found. Statistical arguments favor identification with the SNR N49, located within the box. It is suggested that if N49 was the source of the transient, then peak gamma-ray and hard X-5ay luminosity was between 10 to the 44th and 10 to the 45th ergs/s, and the total radiated energy was between 10 to the 43rd and 10 to the 44th ergs.

Evans, W. D.↗

NASA NTRS2010

Probing the Nature of Short Swift Bursts via Deep INTEGRAL Monitoring of GRB 050925

We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: 1) galactic plane (b=-0.1 deg) localization, 2) 150 msec duration, and 3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than -1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in approximately 5 Ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the H(sub II), regions (W 58) at the galactic longitude of 1=70 deg, we also discuss the source frame properties of GRB 050925.

Sakamoto, T.↗

NASA NTRS1976

A model for the X-ray nova A0620-00

A model is proposed for the transient X-ray source A0620-00 involving a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. A0620-00 should provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗

NASA NTRS1982

The observation of a coronal transient directed at earth

The paper reports the observation of a large coronal transient that can only be interpreted as a three-dimensional structure. Its form is one which has not been observed before: a gradually expanding, sun-centered disk of excess brightness, whose projected radius increased from 4 to 8 solar radii during 0832-0958 UT on November 27, 1979. This earth-directed transient was the source of an interplanetary shock wave that reached ISEE 3 at 0649 UT, November 30, and earth at 0738 UT, November 30. Fitting the shock speed at ISEE 3 and the average transit speed from the sun to ISEE 3 to a power law of the form V = (V sub 0)(r exp -n), it is found that V sub 0 = 1980 km/s and n = 0.294, in good agreement with shock wave models. The shock speed predicted by the power law at 10 solar radii is 1000 km/s, in good agreement with the estimated frontal speed of the transient.

Howard, R. A.↗

NASA NTRS1993

Analysis of a hardware and software fault tolerant processor for critical applications

Computer systems for critical applications must be designed to tolerate software faults as well as hardware faults. A unified approach to tolerating hardware and software faults is characterized by classifying faults in terms of duration (transient or permanent) rather than source (hardware or software). Errors arising from transient faults can be handled through masking or voting, but errors arising from permanent faults require system reconfiguration to bypass the failed component. Most errors which are caused by software faults can be considered transient, in that they are input-dependent. Software faults are triggered by a particular set of inputs. Quantitative dependability analysis of systems which exhibit a unified approach to fault tolerance can be performed by a hierarchical combination of fault tree and Markov models. A methodology for analyzing hardware and software fault tolerant systems is applied to the analysis of a hypothetical system, loosely based on the Fault Tolerant Parallel Processor. The models consider both transient and permanent faults, hardware and software faults, independent and related software faults, automatic recovery, and reconfiguration.

Dugan, Joanne B.↗

NASA NTRS2019

Swift-XRT Follow-up of Gravitational-wave Triggers in the Second Advanced LIGO/Virgo Observing Run

The Neil Gehrels Swift Observatory carried out prompt searches for gravitational-wave (GW) events detected by the LIGO/Virgo Collaboration (LVC) during the second observing run ("O2"). Swift performed extensive tiling of eight LVC triggers, two of which had very low false-alarm rates (GW170814 and the epochal GW170817), indicating a high confidence of being astrophysical in origin; the latter was the first GW event to have an electromagnetic counterpart detected. In this paper we describe the follow-up performed during O2 and the results of our searches. No GW electromagnetic counterparts were detected; this result is expected, as GW170817 remained the only astrophysical event containing at least one neutron star after LVC's later retraction of some events. A number of X-ray sources were detected, with the majority of identified sources being active galactic nuclei. We discuss the detection rate of transient X-ray sources and their implications in the O2 tiling searches. Finally, we describe the lessons learned during O2 and how these are being used to improve the Swift follow-up of GW events. In particular, we simulate a population of gamma-ray burst afterglows to evaluate our source ranking system's ability to differentiate them from unrelated and uncataloged X-ray sources. We find that ≈60%–70% of afterglows whose jets are oriented toward Earth will be given high rank (i.e., "interesting" designation) by the completion of our second follow-up phase (assuming that their location in the sky was observed), but that this fraction can be increased to nearly 100% by performing a third follow-up observation of sources exhibiting fading behavior.

N. J. Klingler↗

NASA NTRS2014

Water Transport and the Evolution of CM Parent Bodies

Extraterrestrial water-bearing minerals are of great importance both for understanding the formation and evolution of the solar system and for supporting future human activities in space. Asteroids are the primary source of meteorites, many of which show evidence of an early heating episode and varying degrees of aqueous alteration. The origin and characterization of hydrated minerals (minerals containing H2O or OH) among both the main-belt and near-earth asteroids is important for understanding a wide range of solar system formation and evolutionary processes, as well as for planning for human exploration. Current hypotheses postulate asteroids began as mixtures of water ice and anhydrous silicates. A heating event early in solar system history was then responsible for melting the ice and driving aqueous alteration. The link between asteroids and meteorites is forged by reflectance spectra, which show 3-μm bands indicative of bound OH or H2O on the C-class asteroids, which are believed to be the parent bodies of the carbonaceous chondrites in our collections. The conditions at which aqueous alteration occurred in the parent bodies of carbonaceous chondrites are thought to be well-constrained: at 0-25 C for less than 15 Myr after asteroid formation. In previous models, many scenarios exhibit peak temperatures of the rock and co-existing liquid water in more than 75 percent of the asteroid's volume rising to 150 C and higher, due to the exothermic hydration reactions triggering a thermal runaway effect. However, even in a high porosity, water-saturated asteroid very limited liquid water flow is predicted (distances of 100's nm at most). This contradiction has yet to be resolved. Still, it may be possible for water to become liquid even in the near-surface environment, for a long enough time to drive aqueous alteration before vaporizing or freezing then subliming. Thus, we are using physics- and chemistry-based models that include thermal and fluid transport as well as the effects of relevant chemical reactions, to investigate whether formation of hydrated minerals can occur in the surface and near-surface environments of carbonaceous type asteroids. These models will elucidate how the conditions within the parent body that cause internal aqueous alteration play themselves out at the asteroid's surface. We are using our models to determine whether the heat budget of 20-100-km bodies is sufficient to bring liquid water to the near-surface and cause mineral alteration, or whether additional heat input at the surface (i.e, by impacts) is needed to provide a transient liquid water source for mineral hydration without large- scale liquid water transport.

Coker, R.↗

NASA NTRS2021

A Comprehensive X-ray Report on AT2019wey

The Galactic low-mass X-ray binary AT2019wey (ATLAS19bcxp, SRGAJ043520.9+552226, SRGEJ043523.3+552234, ZTF19acwrvzk) was discovered as a new optical transient in Dec 2019, and independently as an X-ray transient in Mar 2020. In this paper, we present comprehensive NICER, NuSTAR, Chandra, Swift, and MAXI observations of AT2019wey from ~1 year prior to the discovery to the end of September 2020. AT2019wey appeared as a ~ 1 mCrab source and stayed at this flux density for several months, displaying a hard X-ray spectrum that can be modeled as a power-law with photon index Γ ~ 1.8. In June 2020 it started to brighten and reached ~20 mCrab in ~2 months. The inclination of this system can be constrained to I ≲ 30° by modelling the reflection spectrum. Starting from late-August (~ 59082 MJD), AT2019wey entered into the hard-intermediate state (HIMS), and underwent a few week-long timescale outbursts, where the brightening in soft X-rays is correlated with the enhancement of a thermal component. Low-frequency quasi-periodic oscillation (QPO) was observed in the HIMS. We detect no pulsation and in timing analysis of the NICER and NuSTAR data. The X-ray states and power spectra of AT2019wey are discussed against the landscape of low-mass X-ray binaries.

Individual X-rays↗

NASA NTRS1976

Recurrent X-ray outbursts from Aquila X-1

Aquila X-1 observations by the All Sky Monitor on Ariel 5 are presented. Data is compared with that obtained by rocket survey, and by the Uhuru, OSO 7, and OAO 3 satellites. The variability of brightness is discussed as a connection between dwarf novae and long term transient X ray sources.

Kaluzienski, L. J.↗

NASA NTRS1981

Compact infrared detector

Broadband IR detector integrated into compact package for pollution monitoring and weather prediction is small, highly responsive, and immune to high noise. Sensing material is transparent sheet metalized with reflecting coating and overcoated with black material on same side. Pulse produced by chopping of infrared source beam creates transient "thermal lens" that temporarily defocuses laser beam probe. Detector monitoring beam measures defocusing which parallels infrared intensity.

Gupta, A.↗

NASA NTRS1982

Solar-Array Simulator

A convenient solar-array simulator has been built for testing systems powered by solar cells. Built for evaluating power extension package in Space Shuttle, the circuit produces the V/I curves of photocell sources; even duplicating transient behavior under partial illumination associated with morning and evening penumbra.

Wright, M. C.↗

NASA NTRS1986

A 6 second periodic X-ray source in Carina

A serendipitous source, 1E 1048.1-5937, was discovered during Einstein imaging observations of the Carina nebula. On July 13, 1979, this source had an intensity of 0.14 IPC counts/s, and the signal was 65 percent pulsed with a period of 6.44 s. An earlier observation failed to detect any source with strength greater than 1/10 the above signal. The source is therefore highly variable, perhaps transient. An Exosat observation of this source on June 20, 1985 confirmed the pulse period and refined the source position to an accuracy of 10 arcsec. On the basis of the position, the source is tentatively identified with a V = 19 optical counterpart. The X-ray spectrum is best fitted by a power law with photon index = 2.26 and a column density of 1.6 x 10 to the 22nd atoms/sq cm. The X-ray characteristics are consistent with an accretion-powered Be star binary.

Seward, F. D.↗

NASA NTRS1987

Control considerations for high frequency, resonant, power processing equipment used in large systems

Addressed is a class of resonant power processing equipment designed to be used in an integrated high frequency (20 KHz domain), utility power system for large, multi-user spacecraft and other aerospace vehicles. It describes a hardware approach, which has been the basis for parametric and physical data used to justify the selection of high frequency ac as the PMAD baseline for the space station. This paper is part of a larger effort undertaken by NASA and General Dynamics to be sure that all potential space station contractors and other aerospace power system designers understand and can comfortably use this technology, which is now widely used in the commercial sector. In this paper, we will examine control requirements, stability, and operational modes; and their hardware impacts from an integrated system point of view. The current space station PMAD system will provide the overall requirements model to develop an understanding of the performance of this type of system with regard to: (1) regulation; (2) power bus stability and voltage control; (3) source impedance; (4) transient response; (5) power factor effects, and (6) limits and overloads.

Mildice, J. W.↗

NASA NTRS1986

Gamma-ray burst and spectroscopy instrumentation development at the Goddard Space Flight Center

This paper summarizes the activities that are specifically related to the development of instrumentation for gamma-ray astronomy. Three programs are described: (1) the Gamma-Ray Imaging Spectrometer (GRIS), a balloon-borne array of seven germanium detectors for high-resolution spectrographic studies of persistent gamma-ray sources; (2) the Transient Gamma-Ray Spectrometer (TGRS), a single radiatively-cooled germanium detector for the spectrographic study of gamma-ray bursts, and (3) the Rapidly Moving Telescope (RMT), a ground-based optical telescope for the detection and study of short-lived optical transients, particularly those that occur in coincidence with gamma-ray bursts.

Teegarden, B. J.↗

NASA NTRS1987

Control considerations for high frequency, resonant, power processing equipment used in large systems

Mildice, J. W.↗

NASA NTRS1991

Response of a confined gas to volumetric heating in the absence of gravity. I - Slow transients

A one-dimensional model for bulk motion induced by a transient volumetric heat source in a confined gas at zero gravity is considered. Rational approximation methods are used to derive a quantitative theory for the gas response to a spatiallly distributed, time-dependent internal power deposition. The resulting low Mach number compressible flow equations are solved by using perturbation methods. Solutions are given for a conduction-free core and thin conductive boundary layers adjacent to the end walls. It is found that may any spatially nonuniform power deposition will cause fluid motion. Net mass transport in the closed container will occur for certain spatially distributed heating. The model mimics the thermal effects of an exothermic gas phase reaction in vapor transport experiments conducted in space. The solutions demonstrate that thermally induced mass transport can be as large as diffusive mass transport in a typical experiment.

Herczynski, A.↗

NASA NTRS1992

Highlights of the theoretical work reported at the workshop

A brief overview is given of the theoretical work done on gamma-ray bursts (GRBs) done in this workshop. Papers on energy source models, optical transients, X-ray and gamma-ray continuum models, and cyclotron line models are reviewed.

Lamb, D. Q.↗

NASA NTRS1998

White Dwarf Pulsars

Work on NAG5-3288 ("White Dwarf Pulsars") has been fully integrated with the identically titled project NAG5-4734. The final report below is the same, since the data analysis and interpretative work are integrated, as are the resulting (previous and in-pipeline) publications. The proposal was designed to study pulse and orbital modulations in candidate DQ Herculis stars. Data on 5 stars were obtained. The best results were obtained on YY Draconis, which exhibited a strongly pulsed hard X-ray flux, and even suggested a transition between one-pole and two-pole emission during the course of the observation. This result is being readied for inclusion in a comprehensive study of YY Draconis. A strong pulsation appeared to be present also in H0857-242, but with a period of - 50 minutes, confusion with the first harmonic of the satellite's orbital frequency is possible. So that result is uncertain and is "on ice". A negative result was obtained on 4UO608-49 (V347 Pup), suggesting either that the X-ray identification is incorrect, or that the source is very transient. Finally, data was obtained on V1432 Aql and WZ Sge, respectively the slowest and fastest of these stars. Combined with the ASCA data, the high-energy data demonstrates the latter to contain a white dwarf rotating with P = 27.87 s (Patterson et al. 1998, PASP, 110, 403). Optical photometry contemporaneous with the X-ray data was obtained of V1432 Aql, in order to study the variations in the eclipse waveform. As anticipated, the width and centroid of the eclipse appeared to vary with the 50-day "supercycle".

Patterson, Joseph↗