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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The average X-ray/gamma-ray spectra of Seyfert galaxies from Ginga and OSSE and the origin of the cosmic X-ray background

We have obtained the first average 2-500 keV spectra of Seyfert galaxies, using the data from Ginga and Compton Gamma-Ray Observatory's (CGRO) Oriented Scintillation Spectrometer Experiment (OSSE). Our sample contains three classes of objects with markedly different spectra: radio-quiet Seyfert 1's and 2's, and radio-loud Seyfert 1's. The average radio-quiet Seyfert 1 spectrum is well-fitted by a power law continuum with the energy spectral index alpha approximately equals 0.9, a Compton reflection component corresponding to a approximately 2 pi covering solid angle, and ionized absorption. There is a high-energy cutoff in the incident power law continuum: the e-folding energy is E(sub c) approximately equals 0.6(sup +0.8 sub -0.3) MeV. The simplest model that describes this spectrum is Comptonization in a relativistic optically-thin thermal corona above the surface of an accretion disk. Radio-quiet Seyfert 2's show strong netural absorption, and there is an indication that their X-ray power laws are intrinsically harder. Finally, the radio-loud Seyfert spectrum has alpha approximately equals 0.7, moderate neutral absorption E(sub C) = 0.4(sup +0.7 sub -0.2) MeV, and no or little Compton reflection. This is incompatible with the radio-quiet Seyfert 1 spectrum, and probably indicating that the X-rays are beamed away from the accretion disk in these objects. The average spectra of Seyferts integrated over redshift with a power-law evolution can explain the hard X-ray spectrum of the cosmic background.

Zdziarski, Andrzej A.↗
NASA NTRS1995

Observations and theory of X-rays and gamma-rays from radio-quiet Seyferts

Recent oriented scintillation spectrometer experiment (OSSE) observations of sift gamma-ray emission from radio-quiet Seyfert galaxies as well as their theoretical implications are reviewed. For some Seyferts, the OSSE data can be combined with X-ray data from Ginga and ROSAT. Seyfert 1s have intrinsic power-law spectra with approximately 0.9 extending without a break to at least approximately 200 keV. There is some evidence for a break at higher energies. On top of this intrinsic spectrum there is a Compton reflection component, which corresponds to cold matter covering a approximately 2 pi solid angle as seen by the power-law source. Compton reflection is responsible for a hardening of the spectrum in the approximately 5-30 keV range and a softening at approximately 30-200 keV. This spectrum is then abasorbed by a partially ionized external medium. The spectra of Seyfert 2s are marginally consistent with those of Seyfert 1s modified by strong absorption. However, there are indications that their intrinsic X-ray spectra are harder than those of Seyfert 1s. This is in fact the case for NGC 4151, a Seyfert 1.5. The Seyfert spectra integrated over redshift with cosmological evolution can explain the cosmic X-ray background spectrum from 1 to 100 keV.

Zdziuarski, A. A.↗
NASA NTRS1995

The nuclear X-ray source in NGC 3628: A strange active galactic nucleus or the most luminous high-mass X-ray binary known?

After 12 years, during which its unabsorbed soft X-ray flux in the 0.1-2.0 keV band was almost constant at about f(sub x) approximately 10(exp -12) ergs/s/sq cm, the compact nuclear source in NGC 3628 was not detected in one of our ROSAT observations, with a limiting sensitivity of f(sub x) approximately 5 x 10(exp -14) ergs/s/sq cm. Our data can be explained in two ways. The source is either the most massive X-ray binary known so far, with a greater than and approximately equal to 75 solar mass black hole, or an unusual low-luminosity Active Galactic Nuclei (AGN). The X-ray spectrum is typical of a high-mass X-ray binary, while the luminosity of the source of L(sub x) is approximately equal to 10(exp 40) ergs/s is more similar to those of low-luminosity AGNs. If it is an AGN, variable obscuration might explain the observed light curve.

Dahlem, Michael↗
NASA NTRS1997

Testing the Pairs-Reflection Model with X-Ray Spectral Variability and X-Ray Properties of Complete Samples of Radio-Selected BL Lacertae Objects

This grant was awarded to Dr. C. Megan Urry of the Space Telescope Science Institute in response to two successful ADP proposals to use archival Ginga and Rosat X-ray data for 'Testing the Pairs-Reflection model with X-Ray Spectral Variability' (in collaboration with Paola Grandi, now at the University of Rome) and 'X-Ray Properties of Complete Samples of Radio-Selected BL Lacertae Objects' (in collaboration with then-graduate student Rita Sambruna, now a post-doc at Goddard Space Flight Center). In addition, post-docs Joseph Pesce and Elena Pian, and graduate student Matthew O'Dowd, have worked on several aspects of these projects. The grant was originally awarded on 3/01/94; this report covers the full period, through May 1997. We have completed our project on the X-ray properties of radio-selected BL Lacs.

Urry, C. Megan↗
NASA NTRS1998

Long Term Hard X-ray Monitoring of X-ray Bursters

This grant supported our analysis of BATSE occultation data on x-ray bursters and neutron star low mass x-ray binaries (LMXBs) from the Compton Gamma-ray Observatory carried out under observing cycle 6. The work carried out under this grant was closely related to our separate investigation (NAG5-3808) to develop a prototype BATSE imaging survey for faint transients. In this Final Report, we summarize the Scientific Objectives of this investigation of hard x-ray studies of bursters and the Results Achieved; and finally the Papers Published.

Grindlay, Jonathan E.↗
NASA NTRS1996

Design, Fabrication and Testing of Multilayer Coated X-Ray Optics for the Water Window Imaging X-Ray Microscope

Hoover et. al. built and tested two imaging Schwarzschild multilayer microscopes. These instruments were constructed as prototypes for the "Water Window Imaging X-Ray Microscope," which is a doubly reflecting, multilayer x-ray microscope configured to operate within the "water window." The "water window" is the narrow region of the x-ray spectrum between the K absorption edges of oxygen (lamda = 23.3 Angstroms) and of carbon (lamda = 43.62 Angstroms), where water is relatively highly transmissive and carbon is highly absorptive. This property of these materials, thus permits the use of high resolution multilayer x-ray microscopes for producing high contrast images of carbon-based structures within the aqueous physiological environments of living cells. We report the design, fabrication and testing of multilayer optics that operate in this regime.

Spencer, Dwight C.↗
NASA NTRS1998

A Three-Dimensional Analysis of the Galactic Gamma-Ray Emission Resulting from Cosmic-Ray Interaction with the Interstellar Gas and Radiation Fields

This final report outlines the progress of the contractor's support for the analysis of data under ADP (NRA 96-ADP-08; Proposal No. 167-96 adp). The primary task object was to construct a 3-D model for the distribution of high-energy (20 MeV-30 GeV) gamma-ray emission in the Galactic disk. Under this task the contractor was to utilize data from the EGRET instrument on the Compton Gamma-Ray Observatory, HI and CO surveys, radio-continuum surveys at 408 MHz, 1420 MHz, 5 GHz, and 19 GHz, the COBE Diffuse Infrared Background Experiment (DIRBE) all-sky maps from I to 240 um, and ground-based B,V, J, H and K photometry. The respective contributions to the high-latitude gamma-ray emission from cosmic ray-matter interactions, inverse Compton scattering, and extra-galactic emission were to be determined.

Sodraski, Thomas J.↗
NASA NTRS1998

Studying the High Energy Gamma Ray Sky with Gamma Ray Large Area Space Telescope (GLAST)

Building on the success of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory, the Gamma Ray Large Area Space Telescope (GLAST) will make a major step in the study of such subjects as blazars, gamma Ray bursts, the search for dark matter, supernova remnants, pulsars, diffuse radiation, and unidentified high energy sources. The instrument will be built on new and mature detector technologies such as silicon strip detectors, low-power low-noise LSI, and a multilevel data acquisition system. GLAST is in the research and development phase, and one full tower (of 25 total) is now being built in collaborating institutes. The prototype tower will be tested thoroughly at Stanford Linear Accelerator Center (SLAC) in the fall of 1999.

Kamae, T.↗
NASA NTRS1998

Identification of the Periodic Hard X-Ray Transient GRO J1849-03 with the X-Ray Pulsar GS 1843-02 = X1845-024: A New Be/X-Ray Binary

We identify the periodic transient hard X-ray source GRO J1849-03 with the transient x-ray pulsar GS 1843-02 = X1845-024 based on the detection of x-ray outbursts from X1845-024 coincident with hard x-ray outbursts of GRO J1849-03. Based on its spin period of 94.8 s and its orbital period of 241 days, we classify the system as a Be/X-ray binary.

Soffitta, P.↗
NASA NTRS1998

Radio and X-Ray Observations of the 1998 Outburst of the Recurrent X-Ray Transient 4U 1630-47

We report radio (VLA and ATCA), soft X-ray (RXTE ASM), and hard X-ray (CGRO BATSE) observations of a 1998 outburst in the recurring X-ray transient 4U 1630-47 where radio emission was detected for the first time. The radio observations identify the position of 4U 1630-47 to within 1". Because the radio emission is optically thin with a spectral index of approximately -0.6 during the rise and approximately -1 during the peak and decay of the initial radio event, the emission is probably coming from an optically thin radio jet ejected over a period of time. The 20-100 keV emission first appeared 1998 January 28 (MJD 50841), the 2-12 keV emission first appeared February 3 (MJD 50847), and the first radio emission was detected February 12.6 (MJD 50856.6). The rise of the radio emission probably began about February 7 (MJD 50851) when the X-rays were in a very hard, fluctuating hardness state, just before changing to a softer, more stable hardness state.

Hjellming, R. M.↗
NASA NTRS1999

Remote X-Ray Diffraction and X-Ray Fluorescence Analysis on Planetary Surfaces

The legacy of planetary X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) began in 1960 when W. Parish proposed an XRD instrument for deployment on the moon. The instrument was built and flight qualified, but the Lunar XRD program was cancelled shortly before the first human landing in 1969. XRF chemical data have been collected in situ by surface landers on Mars (Viking 1 & 2, Pathfinder) and Venus (Venera 13 & 14). These highly successful experiments provide critical constraints on our current understanding of surface processes and planetary evolution. However, the mineralogy, which is more critical to planetary surface science than simple chemical analysis, will remain unknown or will at best be imprecisely constrained until X-ray diffraction (XRD) data are collected. Recent progress in X-ray detector technology allows the consideration of simultaneous XRD (mineralogic analysis) and high-precision XRF (elemental analysis) in systems miniaturized to the point where they can be mounted on fixed landers or small robotic rovers. There is a variety of potential targets for XRD/XRF equipped landers within the solar system, the most compelling of which are the poles of the moon, the southern highlands of Mars and Europa.

Blake, David F.↗
NASA NTRS2001

Chandra X-Ray Observations of the Anomalous X-Ray Pulsar 1E 2259+58.6

We present X-ray imaging, timing, and phase resolved spectroscopy of the anomalous X-ray pulsar 1E 2259+58.6 using the Chandra X-ray Observatory. Time resolved X-ray spectra show no significant variation as a function of pulsar spin phase. The phase averaged spectrum is well described by a powerlaw plus blackbody model; we find no evidence for spectral features. We derive a spin period. We have detected a halo beyond the central source, possibly due to dust scattering in the ISM (interstellar matter).

Patel, Sandeep K.↗
NASA NTRS2002

Design and Development of Thin Plastic Foil, Conical Approximation, High Through-out X-Ray Telescope: Light Weight, Thin Plastic Foil, X-Ray Telescopes

We present results from a program to develop an X-ray telescope made from thin plastic shells. Our initial results have been obtained from multi-shell cylindrical lenses that are used in a point-to-point configuration to image the small focal spot of a an X-ray tube on a microchannel plate detector. We describe the steps that led up to the present design and present data from the tests that have been used to identify the properties of the plastic material that make it a suitable X-ray reflector. We discuss two applications of our technology to X-ray missions that are designed to address some of the scientific priorities set forth in NASA's long term plans for high energy astrophysics. One mission will observe in the 1 - 10 keV band, the other will extend up to ca. 100 keV.

Schnopper, Herbert W.↗
NASA NTRS2001

Discovery of Nearly Coherent Oscillations with a Frequency of approximately 567 Hz During Type I X-ray Bursts of the X-ray Transient and Eclipsing Binary X1658-298

We report the discovery of nearly coherent oscillations with a frequency of approximately 567 Hz during type I X-ray bursts from the X-ray transient and eclipsing binary X1658-298. If these oscillations are directly related to the neutron star rotation, then the spin period of the neutron star in X1658-298 is approximately 1.8 ms. The oscillations can be present during the rise or decay phase of the bursts. Oscillations during the decay phase of the bursts show an increase in frequency of approximately 0.5-1 Hz. However, in one particular burst the oscillations reappear at the end of the decay phase at about 571.5 Hz. This represents an increase in oscillation frequency of about 5 Hz, which is the largest frequency change seen so far in a burst oscillation. It is unclear if such a large change can be accommodated by present models used to explain the frequency evolution of the oscillations. The oscillations at 571.5 Hz are unusually soft compared to the oscillations found at 567 Hz. We also observed several bursts during which the oscillations are detected at much lower significance or not at all. Most of these bursts happen during periods of X-ray dipping behavior, suggesting that the X-ray dipping might decrease the amplitude of the oscillations (although several complications exist with this simple picture). We discuss our discovery in the framework of the neutron star spin interpretation.

Wijnands, Rudy↗
NASA NTRS2003

Investigation of Solar Flares Using Spectrally, Spatially, and Temporally Resolved Observations in Gamma Rays, Hard X Rays, and Microwaves

The high-energy components of solar flares radiate at a wide range of wavelengths. We are using spatially, spectrally, and temporally resolved hard X-ray, gamma-ray, and microwave observations of solar flares to investigate flare models and to understand the flare acceleration process. The hard X-ray and gamma-ray observations are obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft that was launched on February 5, 2002. The microwave observations are obtained with the Owens Valley Radio Observatory (OVRO), which has been dedicated to daily observations of solar flares in microwaves with a five-element interferometer since June 1992. These studies are expected to yield exciting new insights into the fundamental physics of the flare acceleration processes.

Crannell, Carol Jo↗
NASA NTRS2003

Hard X-Ray, Soft X-Ray, and EUV Studies of Solar Eruptions

Document study the hard X-ray (HXR), soft X-ray (SXR) ,EUV, and magnetic nature of solar eruptions, with the objective of elucidating the physics of the eruption process. In particular, it was examine the viability of two specific eruption mechanisms, detailed in our proposal. These mechanisms are the "breakout model", and the "tether cutting model". During the second year, it was a significant progress in the goals to Data Sets Utilized. In the publications during this second year of the grant period, the data was used from the E W Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) instruments on SOHO, and from the Soft X-ray Telescope (SXT), Hard X-ray Telescope (HXT), and the Bragg Crystal Spectrometer (BCS) on Yooh.

Sterling, Alphonse C.↗
NASA NTRS2004

X-Ray Weak Broad-Line Quasars: Absorption or Intrinsic X-Ray Weakness

XMM observations of X-ray weak quasars have been performed during 2003. The data for all but the last observation are now available (there has been a delay of several months on the initial schedule, due to high background flares which contaminated the observations: as a consequence, most of them had to be rescheduled). We have reduced and analyzed these data, and obtained interesting preliminary scientific results. Out of the eight sources, 4 are confirmed to be extrimely X-ray weak, in agreement with the results of previous Chandra observations. 3 sources are confirmed to be highly variable both in flux (by factors 20-50) and in spectral properties (dramatic changes in spectral index). For both these groups of objects, an article is in preparation. Preliminary results have been presented at an international workshop on AGN surveys in December 2003, in Cozumel (Mexico). In order to further understand the nature of these X-ray weak quasars, we submitted proposals for spectroscopy at optical and infrared telescopes. We obtained time at the TNG 4 meter telescope for near-IR observations, and at the Hobby-Eberly Telescope for optical high-resolution spectroscopy. These observations will be performed in early 2004, and will complement the XMM data, in order to understand whether the X-ray weakness of these sources is an intrinsic property or is due to absorption by circumnuclear material.

Risaliti, Guido↗
NASA NTRS2004

The Distribution of Cosmic-Ray Sources in the Galaxy, Gamma-Rays and the Gradient in the CO-to-H2 Relation

We present a solution to the apparent discrepancy between the radial gradient in the diffuse Galactic gamma-ray emissivity and the distribution of supernova remnants, believed to be the sources of cosmic rays. Recent determinations of the pulsar distribution have made the discrepancy even more apparent. The problem is shown to be plausibly solved by a variation in the Wco-to-N(H2) scaling factor. If this factor increases by a factor of 5-10 from the inner to the outer Galaxy, as expected from the Galactic metallicity gradient and supported by other evidence, we show that the source distribution required to match the radial gradient of gamma-rays can be reconciled with the distribution of supernova remnants as traced by current studies of pulsars. The resulting model fits the EGRET gamma-ray profiles extremely well in longitude, and reproduces the mid-latitude inner Galaxy intensities better than previous models.

Strong, A. W.↗