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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 109 records · Page 6
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NASA NTRS1977

X-ray spectra of Hercules X-1. 1: Iron line fluorescence from a subrelativistic shell

The X-ray spectrum of Hercules X-1 was observed in the energy range 2-24 keV from August 29 to September 3, 1975. A broad iron line feature is observed in the normal high state spectrum. The line equivalent width is given along with its full-width-half-maximum energy. Iron line fluorescence from an opaque, cool shell of material at the Alfven surface provides the necessary luminosity in this feature. The line energy width can be due to Doppler broadening if the shell is forced to corotate with the pulsar at a radius 800 million cm. Implications of this model regarding physical conditions near Her X-1 are discussed.

Pravdo, S. H.↗
NASA NTRS1977

X-ray spectra of Hercules X-1. I - Iron line fluorescence from a subrelativistic shell

The X-ray spectrum of Her X-1 was observed in the energy range from 2 to 24 keV from August 29 to September 3, 1975. Emission features are observed near the K-alpha iron-line energy which exhibit both broadening and a double line structure. The total luminosity in these features is about 4 by 10 to the 35th power ergs/s. Iron line fluorescence from an opaque cool (not exceeding 1 million K) shell of material at the Alfven surface provides the necessary luminosity in this feature. The double line structure and the line energy width can be due to Doppler shifts if the shell is forced to corotate with the pulsar at a radius of at least 800 million cm. Implications of this model regarding physical conditions near Her X-1 are discussed.

Pravdo, S. H.↗
NASA NTRS1994

X-Ray Absorption Spectroscopy in High Temperature Oxidation of Metals and Alloys

An experimental technique is described that allows for the joint study of the kinetics and of the oxide structure during the high temperature oxidation of metal surfaces. Oxygen is supplied at the metal through an electrochemical oxygen pump and the oxygen pressure, at the metal surface, is measured during oxidation by a YSZ (yttria stabilized zirconia) oxygen sensor. XAS (x-ray absorption spectroscopy) is performed in fluorescence mode at the cation K edge and after each oxidation step. An appropriate analysis of the XAS spectra could provide information on both the oxidation kinetics and oxide structure. Experimental data on the high temperature oxidation of nickel, cobalt, and Fe(64%)Ni(36%) alloy, at low oxygen pressure, are reported and analyzed according to the proposed data reduction. These results indicate the presented technique to be particularly suitable for studying the hot corrosion of oxide film too thick for common surface spectroscopy (AUGER, ESCA) and too thin for conventional thermogravimetric technique.

Daniele Gozzi↗
NASA NTRS1979

Charge equilibrium and radiation of low-energy cosmic rays passing through interstellar medium

The charge equilibrium and radiation of an oxygen and an iron beam in the MeV per nucleon energy range, representing a typical beam of low-energy cosmic rays passing through the interstellar medium, are considered. Electron loss of the beam has been taken into account by means of the first Born approximation, allowing for the target atom to remain unexcited or to be excited to all possible states. Electron-capture cross sections have been calculated by means of the scaled Oppenheimer-Brinkman-Kramers approximation, taking into account all atomic shells of the target atoms and capture into all excited states of the projectile. The capture and loss cross sections are found to be within 20%-30% of the existing experimental values for most of the cases considered. Radiation of the beam due to electron capture into the excited states of the ion, collisional excitation, and collisional inner-shell ionization, taking into account the fluorescence yield of the ions, has been considered. Effective X-ray production cross sections and multiplicities for the most energetic X-ray lines emitted by the Fe and O beams have been calculated, and error estimates made for the results.

Rule, D. W.↗
NASA NTRS1979

Iron lines from X-ray binaries

A summary of the observational evidence of iron lines from satellite X-ray detectors and binary X-ray pulsars is presented. The current theories consider that the continua X-rays from X-ray pulsars originate at or near the surface of neutron stars, and they can then heat or fluoresce iron ions in surrounding physical regions to create the observed emission. Measurements of the line energy, intensity, and width, and the phase dependence of these quantities can help determine the relative importance of contributions of relative sources. The evidence is presented that the iron emission from some sources contains more than one component, and the spectra of other X-ray binaries including transients and cataclysmic variables also contain iron lines. Some implications of the observed line emission are discussed.

Pravdo, S. H.↗
NASA NTRS1974

On the possible detection of an energetic photon pulse from the recent supernova in NGC 5253

A diffuse atmospheric fluorescence pulse having the proper signatures of an excitation caused by a fast burst of X-ray photons incident from the general direction of the recent supernova in NGC 5253, was recorded on May 3, 1972, at 20 hr 48 min 51 sec UT. Due to excessive background pulses of terrestrial origin, it is concluded that the evidence should at best be regarded as suggestive. It is recommended that the data of satellite-borne X-ray detectors be examined for anomalies at the indicated time.

Ogelman, H.↗
NASA NTRS1978

The X-ray emitting galaxy Centaurus A

OSO-8 X-ray observations of Cen A in 1975 and 1976 are reported. The source spectrum can be well fitted in both years by a power law of number index 1.66 and absorption due to 1.3 by 10 to the 23rd power atoms/sq cm. The total flux varied by a factor of 2 between 1975 and 1976. In 1976 there were flux variations of approximately 40% on a time scale of days. Measurements of the 6.4-keV Fe fluorescent line and the 7.1-keV absorption edge imply Fe/H of approximately 0.000016. Simultaneous radio measurements show variation in phase with X-ray variability. Consideration of radio, millimeter, infrared, and X-ray data shows that all the data can be accounted for by a model in which the X-rays are due to a synchrotron self-Compton source embedded in a cold H2 cloud.

Mushotzky, R. F.↗
NASA NTRS1977

Ultraviolet observations of 3C 273 by the ANS

Five-band spectrophotometry between rest wavelengths of 1340 A and 2850 A is presented. The 2200-A absorption feature seems to be present in 3C 273 with a depth appropriate for an internal reddening of E(B-V) = 0.13. The dereddened ultraviolet flux distribution can be described by a power law of spectral index 1.21. This power law can account for the observed flux in X-rays. It provides more photons than needed to excite the observed H-beta by photoionization and Fe II lines by resonance fluorescence. The emission-line flux ratios, Ly-alpha/C IV/ semiforbidden C III/H-beta are 100/80/60/10.

Wu, C.-C.↗
NASA NTRS1977

The X-ray emitting galaxy Cen-A

OSO-8 X-ray observations of Cen-A in 1975 and 1976 are reported. The source spectrum is well fit in both years by a power law of number index 1.62 and absorption due to 1.3 x 10 to the 23rd power at/sq cm. The total flux varied by a factor 2 between 1975 and 1976. In 1976 there were approximately 40% flux variations on a time scale of days. The 6.4 keV Fe fluorescent line and the 7.1 keV absorption edge were measured implying Fe/H approximately equals .000016. Simultaneous radio measurements show variation in phase with X-ray variability. Models considering radio, milimeter, IR and X-ray data show that all the data can be accounted for by a model in which the X-rays are due to a synchrotron self-Compton source embedded in a cold H(2) cloud.

Mushotzky, R. F.↗
NASA NTRS1978

X-ray observations of a flare in NGC4151 from OSO-8

The 2-60 keV flux from NGC4151 changed by a factor of two on a timescale of 1.5 days. No fluctuations were detected in excess of a factor of three on timescales less than four hours. During a total observation of approximately 11 days there were no statistically significant changes in spectral shape. The spectrum was fitted by a power law with photon index alpha approximately 1.42 + or - 0.06 and column density N sub H approximately 7.5 + or - 0.5 x 10 to the 22d power at/cu cm. A 2 sigma residual to this fit implies fluorescent Fe line emission with E. W. approximately 240 eV. Both synchrotron self-Compton and thermal Compton models are consistent with the X-ray data.

Mushotzky, R. F.↗
NASA NTRS1977

X-ray sources in stellar winds

A model of a binary X-ray source immersed in a stellar wind from its companion star is considered. The geometry of the constant ionization and temperature contours in the model is discussed, and X-ray radiative transfer through the wind is described. The results are applied to make predictions about the presence and variability of iron K-shell fluorescence lines, to explain the light curve of Cen X-3 during a 'low' to 'high' state transition in July 1972, and to predict variability with orbital phase of resonance ultraviolet lines such as N V at 1238 and 1242 A from the binary system.

Hatchett, S.↗
NASA NTRS1978

X-ray observations of a flare in NGC 4151 from OSO 8

The 2-60-keV flux from NGC 4151 has been observed to change by a factor of 2 on a time scale of 1.5 days. No fluctuations in excess of a factor of 3 are detected on time scales less than 4 hours. During a total observation of approximately 11 days there were no statistically significant changes in spectral shape. The spectrum can be fitted by a power law with photon index of about 1.42 + or - 0.06 and a hydrogen column density of approximately 7.5 + or - 0.5 x 10 to the 22nd power atoms/sq cm. A 2-sigma residual to this fit implies fluorescent Fe line emission with an equivalent width of about 240 eV. Both synchrotron self-Compton and thermal Compton models are consistent with the X-ray data.

Mushotzky, R. F.↗
NASA NTRS1975

On the origin of 4640-4650 A emission in X-ray stars

The origin is investigated for a prominent and rapidly variable emission feature near the 4640-A line which has been observed in the optical counterparts of Sco X-1, Cyg X-2, Her X-1, Cen X-3, 3U 0900-40, and 3U 1700-37. It is suggested that the emission is generated in the vicinity of a compact X-ray source by the interaction of X-rays with nearby gaseous matter and that three likely sources of the emission are the ions C III, N III, and O II. Results are presented for a detailed mathematical model of an X-ray source surrounded by a uniform distribution of matter and are used to evaluate possible emission mechanisms. It is concluded that selective emission of N III (4634 to 4641 A) in the Bowen fluorescence process may be the responsible mechanism.

Mcclintock, J. E.↗
NASA NTRS2020

The Slow Demise of the Long-Lived Sn 2005ip

The Type IIn supernova (SN IIn) 2005ip is one of the most well-studied and long-lasting examples of an SN interacting with its circumstellar environment. The optical light curve plateaued at a nearly constant level for more than five years, suggesting ongoing shock interaction with an extended and clumpy circumstellar medium (CSM). Here, we present continued observations of the SN from ∼1000 to 5000 d post-explosion at all wavelengths, including X-ray, ultraviolet, near-infrared (NIR), and mid-infrared. The UV spectra probe the pre-explosion mass loss and show evidence for CNO processing. From the bolometric light curve, we find that the total radiated energy is in excess of 10 50 erg, the progenitor star’s pre-explosion mass-loss rate was >~ 1 × 10 −2 Mꙩ yr −1 , and the total mass lost shortly before explosion was >~1Mꙩ, though the mass lost could have been considerably larger depending on the efficiency for the conversion of kinetic energy to radiation. The ultraviolet through NIR spectrum is characterized by two high-density components, one with narrow high-ionization lines, and one with broader low-ionization H I, He I, [OI], Mg II, and Fe II lines. The rich Fe II spectrum is strongly affected by Lyα fluorescence, consistent with spectral modelling. Both the Balmer and He I lines indicate a decreasing CSM density during the late interaction period. We find similarities to SN 1988Z, which shows a comparable change in spectrum at around the same time during its very slow decline. These results suggest that, at long last, the shock interaction in SN 2005ip may finally be on the decline.

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