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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Observations of the highly variable X-ray source GX 339-4.

Observations with the MIT experiment on the OSO-7 have led to the discovery of an X-ray source, GX 339-4, which varies in intensity by at least a factor of 60 over hundreds of days but shows no evidence of periodic behavior or abrupt intensity changes on time scales from 3 minutes to 13 days. The observations show intense high states, low states with spectra consistent with increased absorption, and off states, when no statistically significant signal is observed. The behavior is unlike that of any previously reported X-ray source.

Markert, T. H.↗
DOE OSTI2019

Monitoring, Understanding, and Predicting the Growth of Methane Emissions in the Arctic

Concern over Arctic methane (CH 4 ) emissions has increased following recent discoveries of poorly understood sources and predictions that methane emissions from known sources will grow as Arctic temperatures increase. New efforts are required to detect increases and explain sources without being confounded by the multiple sources. Methods for distinguishing different sources are critical. We conducted measurements of atmospheric methane and source tracers and performed baseline global atmospheric modeling to begin assessing the climate impact of changes in atmospheric methane. The goal of this project was to address uncertainties in Arctic methane sources and their potential impact on climate by (1) deploying newly developed trace-gas analyzers for measurements of methane, methane isotopologues, ethane, and other tracers of methane sources in the Barrow, AK, (2) characterizing methane sources using high-resolution atmospheric chemical transport models and tracer measurements, and (3) modeling Arctic climate using the state-of-the-art high- resolution Spectral Element Community Atmosphere Model (CAM-SE).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

The ZTF Source Classification Project. I. Methods and Infrastructure

The Zwicky Transient Facility (ZTF) has been observing the entire northern sky since the start of 2018 down to a magnitude of 20.5 (5σ for 30 s exposure) in the g, r, and i filters. Over the course of two years, ZTF has obtained light curves of more than a billion sources, each with 50–1000 epochs per light curve in g and r, and fewer in i. To be able to use the information contained in the light curves of variable sources for new scientific discoveries, an efficient and flexible framework is needed to classify them. In this paper, we introduce the methods and infrastructure that will be used to classify all ZTF light curves. Our approach aims to be flexible and modular and allows the use of a dynamical classification scheme and labels, continuously evolving training sets, and the use of different machine-learning classifier types and architectures. Finally with this setup, we are able to continuously update and improve the classification of ZTF light curves as new data become available, training samples are updated, and new classes need to be incorporated.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Variations in the Width, Density, and Direction of the Palomar 5 Tidal Tails

Stars that escape globular clusters form tidal tails that are predominantly shaped by the global distribution of mass in the Galaxy, but also preserve a historical record of small-scale perturbations. Using deep grz photometry from DECaLS, we present highly probable members of the tidal tails associated with the evaporating globular cluster Palomar 5. These data yield the cleanest view of a stellar stream beyond ≈20 kpc and reveal: (1) a wide, low surface-brightness extension of the leading tail; (2) significant density variations along the stream; and (3) sharp changes in the direction of both the leading and the trailing tail. In the fiducial Milky Way model, a rotating bar perturbs the Palomar 5 tails and can produce streams with similar width and density profiles to those observed. However, the deviations of the stream track in this simple model do not match those observed in the Palomar 5 trailing tail, indicating the need for an additional source of perturbation. These discoveries open up the possibility of measuring the population of perturbers in the Milky Way, including dark-matter subhalos, with an ensemble of stellar streams and deep photometry alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Discovery of coherent pulsations from the ultraluminous X-ray source NGC 7793 P13

We report the detection of coherent pulsations from the ultraluminous X-ray source (ULX) NGC 7793 P13. The ≈0.42 s nearly sinusoidal pulsations were initially discovered in broadband X-ray observations using XMM-Newton and NuSTAR taken in 2016. We subsequently also found pulsations in archival XMM-Newton data taken in 2013 and 2014. The significant (≫5σ) detection of coherent pulsations demonstrates that the compact object in P13 is a neutron star, and given the observed peak luminosity of ≈10{sup 40} erg s{sup −1} (assuming isotropy), it is well above the Eddington limit for a 1.4 M{sub ⊙} accretor. This makes P13 the second ULX known to be powered by an accreting neutron star. The pulse period varies between epochs, with a slow but persistent spin-up over the 2013–2016 period. This spin-up indicates a magnetic field of B ≈ 1.5 × 10{sup 12} G, typical of many Galactic accreting pulsars. The most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Discovery of optical bursts from an X-ray burst source, MXB1735-44

The optical counterpart of 4U 1735-44, X-ray burst source MXB 1735-44, was studied with the 1.5-m telescope at Cerro Tololo, and by SAS 3, during the period between June 1 and 3, 1978. Explanations for the optical activity are discussed in terms of accretion instabilities onto a neutron star, or thermonuclear flashes on the neutron star itself. Attention is given to the timing of the bursts, which indicate that the burst source probably is located in a region within 1-2 light seconds from the X-ray source. In the binary case, it is noted that the optical emission is probably removed from the X-ray heated stellar atmosphere of the possible companion.

Grindlay, J. E.↗
NASA NTRS1980

A global biogeocenotical biosphere simulation

This model of the D. Forrester type, constructed in differential equations, predicts the food and mineral supply for the factors biosphere population, depending on two socio-economic factors, until about the year 2500. If contemporary rates of natural resources utilization are maintained and there is no management of the environment, food resources will begin to limit human population growth after 2200, and mineral resources will after 2300. A decrease in the biosphere pollution, increase in effective agricultural production, and discovery of new energy sources may forestall or completely avert the onset of a crisis situation. Conservation measures, according to the model, are to a considerable extent realizable only if carried out simultaneously in both areas.

Moiseyev, N. N.↗
NASA NTRS1987

A lunar laboratory

An international research laboratory can be established on the Moon in the early years of the 21st Century. It can be built using the transportation system now envisioned by NASA, which includes a space station for Earth orbital logistics and orbital transfer vehicles for Earth-Moon transportation. A scientific laboratory on the Moon would permit extended surface and subsurface geological exploration; long-duration experiments defining the lunar environment and its modification by surface activity; new classes of observations in astronomy; space plasma and fundamental physics experiments; and lunar resource development. The discovery of a lunar source for propellants may reduce the cost of constructing large permanent facilities in space and enhance other space programs such as Mars exploration.

Keaton, P. W.↗
NASA NTRS1990

Lunar optical interferometer

Various design configurations of a lunar optical interferometer are examined to determine the interaction of science objectives and the architecture of an instrument that will have 10 microarcsec imaging resolution and 0.1 microarcsec astrometric accuracy. The imaging of the central energy source of AGNs, the discovery of earth-like planets around nearby stars, and the measurement of the proper motion of extragalactic objects to determine the isotropy of the Hubble expansion are some of the observations possible with a lunar interferometer. This interferometer with kilometric baselines and large collecting area will be able to make astronomical observations with angular resolution and sensitivity many orders of magnitude beyond orbital based or earth based instruments.

Shao, M.↗
NASA NTRS2014

SGR J1745-29: Swift Discovery and Monitoring of a New SGR Near Sgr A*

Starting in 2013 February, Swift has been performing short daily monitoring observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to determine whether the cloud interaction leads to an increase in the flux from the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise in the X-ray flux from the region near Sgr A*. Initially thought to be a flare from Sgr A*, detection of a short hard X-ray burst from the same region by the Burst Alert Telescope suggested that the flare was from an unresolved new Soft Gamma Repeater, SGR J1745-29. Here we present the discovery of SGR J1745-29 by Swift, including analysis of data before, during, and after the burst. We cover the entire light-curve of the SGR outburst so far, from discovery through to the source entering a Swift Sun constraint in November 2013. Thanks to the interest in G2 and its location near the Galactic Center, SGR J1745-29 has become one of the best monitoring SGRs in outburst yet seen.

Kennea, Jamie A.↗
NASA NTRS2016

Discovery of Coherent Pulsations from the Ultraluminous X-Ray Source NGC 7793 P13

We report the detection of coherent pulsations from the ultraluminous X-ray source (ULX) NGC 7793P13. The approx. =0.42 s nearly sinusoidal pulsations were initially discovered in broadband X-ray observations using XMM-Newton and NuSTAR taken in 2016. We subsequently also found pulsations in archival XMM-Newton data taken in 2013 and 2014. The significant (>>5(sigma)) detection of coherent pulsations demonstrates that the compact object in P13 is a neutron star, and given the observed peak luminosity of 10(exp 40) erg/ s (assuming isotropy), it is well above the Eddington limit for a 1.4 Stellar Mass accretor. This makes P13 the second ULX known to be powered by an accreting neutron star. The pulse period varies between epochs, with a slow but persistent spin-up over the 2013-2016 period. This spin-up indicates a magnetic field of B1.51012 G, typical of many Galactic accreting pulsars. The most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile.

accretion disks – pulsars: individual (NGC 7793 ↗
NASA NTRS2016

Discovery of Coherent Pulsations from the Ultraluminous X-Ray Source NGC 7793 P13

We report the detection of coherent pulsations from the ultraluminous X-ray source (ULX) NGC 7793 P13. The approximately 0.42s nearly sinusoidal pulsations were initially discovered in broadband X-ray observations using XMM-Newton and NuSTAR taken in 2016. We subsequently also found pulsations in archival XMM-Newton data taken in 2013 and 2014. The significant (>>5 sigma ) detection of coherent pulsations demonstrates that the compact object in P13 is a neutron star, and given the observed peak luminosity of approximately 10 (exp 40) erg s (exp -1) (assuming isotropy), it is well above the Eddington limit for a 1.4 solar mass accretor. This makes P13 the second ULX known to be powered by an accreting neutron star. The pulse period varies between epochs, with a slow but persistent spin-up over the 2013â€"2016 period. This spin-up indicates a magnetic field of B approximately 1.5 x -10 (exp 12) G, typical of many Galactic accreting pulsars. The most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile.

Furst, F.↗
NASA NTRS1979

An intense soft high-latitude X-ray source H2156-304 - A new BL Lacertae object

The discovery of an intense high-latitude soft X-ray source (designated H2156-304) detected with the low-energy detectors of the HEAO A-2 experiment is reported. The error box of the source includes a 14th mag starlike object that may be coincident with the radio source PKS 2155-304 and has been suggested as a BL Lac candidate. Intensity variations of H2156-304 on time scales of about 1 sec to 1 day are discussed, along with a probable flare from the source. The derived energy spectrum of the source is shown to be well fitted by either a two-temperature thermal model with temperatures of 16 million and 1.6 million K or a single power-law model with a spectral index of 2.4 + or - 0.3. Hydrogen column densities of approximately 2.5 x 10 to the 20th and 2.0 x 10 to the 20th H atoms/sq cm are obtained for the two-temperature and power-law models, respectively. The emission mechanism of H2156-304 is considered, and the characteristics of this source are compared with those of three known soft X-ray-emitting BL Lac objects.

Agrawal, P. C.↗
DOE OSTI2013

SUB-PeV NEUTRINOS FROM TeV UNIDENTIFIED SOURCES IN THE GALAXY

The IceCube collaboration discovery of 28 high-energy neutrinos over the energy range 30 TeV {approx}< {epsilon}{sub {nu}} {approx}< 1 PeV, a 4.3{sigma} excess over expected backgrounds, represents the first high-confidence detection of cosmic neutrinos at these energies. In light of this discovery, we explore the possibility that some of the sub-PeV cosmic neutrinos might originate in our Galaxy's TeV unidentified (TeV UnID) sources. While typically resolved at TeV energies, these sources lack prominent radio or X-ray counterparts, and so have been considered promising sites for hadron acceleration within our Galaxy. Modeling the TeV UnID sources as Galactic hypernova remnants, we predict sub-PeV neutrino fluxes and spectra consistent with their contributing a minority of n{sub {nu}} {approx}< 2 of the observed events. This is consistent with our analysis of the spatial distribution of the sub-PeV neutrinos and TeV UnID sources, which finds that a best-fit of one, and maximum of 3.8 (at 90% confidence), of the Almost-Equal-To 16 non-atmospheric sub-PeV neutrinos may originate in the TeV UnID sources, with the remaining 75%-95% of events being drawn from an isotropic background. If our scenario is correct, we expect excess sub-PeV neutrinos to accumulate along the Galactic plane, within |l| {approx}< {+-} 30 Degree-Sign of the Galactic center and in the Cygnus region, as observations by IceCube and other high-energy neutrino facilities go forward. Our scenario also has implications for radio, X-ray, and TeV observations of the TeV UnID sources.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Discovery of X-ray and Optical/Infrared Counterpart of XTE J1906+09

We present the Chandra localization of the transient X-ray source XTE J1906+09 and the discovery of optical and infrared counterparts. We analysed the archival Chandra ACIS-I observations of the region and determined the precise source position, that is 8$\arcmin$ away from position determined with the RXTE/PCA. We performed optical observations of the I field around the new location and identified a coincident ~ optical source (R=18.7). There exists an infrared point source in the Two Micron All Sky Survey catalogue with J=15.2, H=14.2 and K=13.5 whose location is also coincident with our Chandra and optical astrometry solutions. We additionally comment on the likely Be/X-ray binary nature of the system.

Gogus, Ersin↗
NASA NTRS1993

Interpretation of gamma-ray burst source count statistics

Ever since the discovery of gamma-ray bursts, the so-called log N-log S relation has been used for determination of their distances and distribution. This task has not been straightforward because of varying thresholds for the detection of bursts. Most of the current analyses of these data are couched in terms of ambiguous distributions, such as the distribution of Cp/Clim, the ratio of peak to threshold photon count rates, or the distribution of V/Vmax = (Cp/Clim) exp -3/2. It is shown that these distributions are not always a true reflection of the log N-log S relation. Some kind of deconvolution is required for obtaining the true log N-log S. Therefore, care is required in the interpretation of results of such analyses. A new method of analysis of these data is described, whereby the bivariate distribution of Cp and Clim is obtained directly from the data.

Petrosian, Vahe↗