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Long, K. S.

Publications and source records attributed to Long, K. S..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Bragg crystal spectroscopy on the OSO 8 satellite

Results are reported for high-resolution OSO 8 Bragg-crystal spectroscopy of a variety of cosmic X-ray sources in the energy range from 2 to 10 keV. A continuous spectrum of Sco X-1 is examined, and results of a search for narrow line emission due to iron near 6.7 keV are presented for 32 galactic X-ray sources, including Sco X-1, Cyg X-3, and Cen X-3. It is noted that the strongest evidence for iron line emission has been obtained for Cyg X-3 and that evidence for an iron line feature has also been found in the spectrum of Cen X-3.

Long, K. S.↗
NASA NTRS1979

Imaging proportional counter for X-ray astronomy

A position-sensitive proportional counter capable of imaging X-rays (0.1-3 keV) over a 10 cm x 10 cm aperture has been constructed. Positioning is obtained by sensing the signals induced by an X-ray event on the two orthogonal sets of cathode wires. Each cathode is divided into a series of cathode strips, each 0.5 cm wide. An X-ray event induces signals on several adjacent strips. Signals from each cathode strip are amplified separately and then added in an equally weighted and an unequally weighted summing amplifier. The position in each direction is obtained by dividing the output of the unequally weighted summer by that of the equally weighted summer. At 0.94 keV, the accuracy of the position sensing is 190 microns. At the same energy, the energy resolution is approximately 65% (FWHM). The proportional counter system is currently being incorporated into a sounding rocket payload having metal mirror optics, which is being constructed by the X-ray astronomy group at the California Institute of Technology.

Long, K. S.↗
NASA NTRS1979

Prospects for experimental research on black holes in binary systems

Cygnus X-1, the single widely accepted example of a black hole in a binary system, is characterized by unusual X-ray properties. The X-ray spectrum of Cygnus X-1 is not cut off above 20 keV, as in most strong X-ray sources. Recent scintillation counter measurements reveal a power law spectrum extending from 40 to 200 keV with a photon spectral index of approximately 2.2. However, it is not clear that these and other X-ray properties of the system are related to the black-hole nature of Cygnus X-1. It is suggested that without a direct test to show that the mass of the compact object in other systems similar to Cygnus X-1 (Circinus X-1 and GX339-4) exceeds the limit of the neutron star mass, a better understanding of the accretion disk phenomenon must be achieved to demonstrate how the properties peculiar to these systems are related to the black hole nature of the compact object. Current accretion disk models are examined, including the alpha-accretion disk and two-temperature accretion disk models.

Long, K. S.↗
NASA NTRS1978

X-ray spectra of A0620-00 obtained with a Bragg crystal spectrometer

The OSO 8 graphite crystal spectrometer was used to obtain observations, in October 1975 and January 1976, of the transient X-ray source A0620-00, which yield upper limits of no more than about 10 eV to the equivalent widths of narrow emission lines of Si XIII, Si XIV, S XV, and S XVI. Photoionization is unlikely to alter the principal conclusion that the electron scattering in the source is substantial. High-resolution spectra obtained in October 1975 reveal a featureless continuum which is better characterized as blackbody (kT about 0.5 keV) than as thin bremsstrahlung emission.

Long, K. S.↗
NASA NTRS1978

Extended X-ray observations of Scorpius X-1 with a Bragg crystal spectrometer

Observations covering multiple orbital periods of the X-ray source Sco X-1 were carried out in 1975 and 1976 with the graphite crystal spectrometer aboard OSO 8. Time-averaged continuum spectra are featureless and are reasonably well described in terms of a Comptonized thermal bremsstrahlung spectrum in which kT is about 1.5-2 keV and in which the number of electron scatterings that each photon is assumed to have undergone is of the order of 100. Line limits, typically with equivalent widths of a few electron volts, are established for important emission lines of Si XIII, Si XIV, S XV, S XVI, and Fe XXV as a function of binary phase.

Long, K. S.↗
NASA NTRS1978

Silicon X-ray line emission from solar flares and active regions

New observations of solar flare and active region X-ray spectra obtained with the Columbia University instrument on OSO-8 are presented and discussed. The high sensitivity of the graphite crystal panel has allowed both line and continuum spectra to be served with moderate spectral resolution. Observations with higher spectral resolution have been made with a panel of pentaerythritol crystals. Twenty-nine lines between 1.5 and 7.0 A have been resolved and identified, including several dielectronic recombination satellite lines to Si XIV and Si XIII lines which have been observed for the first time. It has been found that thermal continuum models specified by single values of temperature and emission measure have fitted the data adequately, there being good agreement with the values of these parameters derived from line intensity ratios.

Parkinson, J. H.↗
NASA NTRS1978

Search for X-ray polarization in the Crab pulsar

Results of a search for X-ray polarization in the Crab pulsar are presented which were obtained by observing the pulsar at 2.6 and 5.2 keV with identical X-ray polarimeters aboard OSO 8. The polarization in different portions of the X-ray light curve is analyzed, the polarization contribution due to the nebula is removed, and the results of the analysis are given for isolated portions of both the primary pulse and the interpulse at 2.6 and 5.2 keV. No evidence for X-ray polarization is found at the 99% confidence level; 3-sigma upper limits to the polarization at 2.6 keV are given along with the largest polarization allowed at 5.2 keV by the 99% confidence counter. It is noted that the trailing edge of the interpulse at 2.6 keV is 26% polarized at the 92% confidence level, while the 5.2-keV polarization measurement of 40% in the leading edge of the primary pulse is different from zero at 96% confidence. X-ray and optical polarization measurements are compared.

Silver, E. H.↗
NASA NTRS1978

Gamma ray polarimetry

Spectroscopic instruments currently being proposed may possess polarimetric capabilities which sould be nurtured and enhanced to permit characterization of basic emission mechanisms which are impossible using other techniques. Compton scattering and pair production detected the polarization of high energy (E is greater than 50 keV) protons in laboratory experiments. The polarization properties of a detection system consisting of 19 germanium crystals in a closed packed array are examined and the advantages of such a detector over Thompson scattering are discussed. The possiblity of using pair production to detect polarization of high energy gamma rays, and the associated modulation factors are discussed. The central difficulty involved in using pair production polarimeters in astrophysical applications is that the typical opening of the electron or positron direction with respect to the incident photon aircitron is small, of order E/sq mc. Multiple scattering in the material used to convert the photons to an electron positron pair causes deviations in the direction of the electron and positron.

Long, K. S.↗
NASA NTRS1978

Search for X-ray line emission from Cassiopeia A

The large area graphite crystal spectrometer aboard OSO 8 has been used to search for X-ray line emission from Cas A from ions of Si, S, and Fe over the energy band 1.865 to 8 keV. No evidence was obtained for line emission. The upper limits for the Si and S line fluxes are used to establish upper limits on the abundances of these elements. The limit on the Fe line flux is consistent with the strength of the emission feature reported in proportional counter experiments. Questions of nonequilibrium in ionization in Cas A and the effects on X-ray line emission are considered.

Kestenbaum, H. L.↗
NASA NTRS1978

An upper limit to the linear X-ray polarization of Scorpius X-1

A measurement of Sco X-1 with the graphite-crystal polarimeters on the OSO 8 satellite yields upper limits (3 sigmas) to the linear polarization of 2.7% and 4.9% at 2.6 keV and 5.2 keV, respectively. The results are discussed in terms of an accretion-disk model.

Weisskopf, M. C.↗
NASA NTRS1978

The application of a drift multiwire proportional counter to the imaging of low energy X-rays

A 75 mm x 75 mm multiwire proportional counter (MWPC) with a 1 micron polypropylene window has been built to map low energy X-rays. The MWPC is constructed with a large drift region which allows us to use the center-of-gravity technique to improve the counter's efficiency and position resolution. Using 330 torr of propane as the gas fill and an anode plane composed of 20 micron diameter Au-plated tungsten wire spaced 1 mm apart, a position resolution of better than 240 microns (FWHM) in two orthogonal directions at an X-ray energy of 0.94 keV has been achieved.

Ku, W. H.-M.↗
NASA NTRS1978

A precision measurement of the X-ray polarization of the Crab Nebula without pulsar contamination

The linear X-ray polarization of the Crab Nebula has been precisely measured at 2.6 keV and 5.2 keV with the OSO 8 graphite crystal polarimeters. The 1.4 ms time resolution of these instruments permitted the removal of any contribution to the polarization from the pulsar. The nebular polarization is 19.2% plus or minus 1.0% at a position angle of 156.4 plus or minus 1.4 deg at 2.6 keV. At 5.2 keV the corresponding results are 19.5% plus or minus 2.8% at 152.6 plus or minus 4.0 deg.

Weisskopf, M. C.↗
NASA NTRS1978

The OSO-8 mosaic graphite stellar X-ray polarimeter

The OSO 8 satellite, launched on June 21, 1975, contains two X-ray polarimeters. These polarimeters use mosaic crystals of graphite to yield polarization-sensitive Bragg reflection of stellar X-rays. The crystals reflect a narrow energy bandwidth centered at 2.6 and 5.2 keV. The polarimeter background signal is minimized by mounting the crystals on parabolic surfaces which focus the diffracted X-rays onto small-area beryllium-window proportional counters. This technique permits the observation of low-intensity X-ray sources and reduces the possibility of systematic background effects which could lead to a false signature of polarization. A description of the instrument is given, and preliminary results for the Crab Nebula and Cyg X-1 are presented.

Novick, R.↗
NASA NTRS1977

Search for thermal X-ray line emission from the Crab Nebula

Observations of the Crab Nebula from 1.85 to 8 keV obtained with the large-area graphite crystal spectrometer on OSO-8 show a smooth featureless continuum with an absence of X-ray emission lines from highly ionized Si and S. Upper limits on the line emission are used to derive an upper limit to the emission measure for a thermal source associated with the Crab Nebula. Existing evidence for an extended thermal source is discussed, and it is shown that the evidence is not contradicted by the upper limits set with the spectrometer data.

Kestenbaum, H. L.↗
NASA NTRS1977

Search for X-ray polarization in Cygnus X-1

Cygnus X-1 was observed at 2.6 and 5.2 keV during a three-day period in November 1975 by the X-ray polarimeters on the OSO-8 satellite. At the 99% confidence level, the results are consistent with the source being unpolarized. Positive evidence for polarization at 2.6 keV was obtained at the 96% confidence level.

Weisskopf, M. C.↗
NASA NTRS1977

A study of four soft X-ray enhancements

Four enhanced regions of diffuse X-ray emission are studied in the 0.15-2 KeV band. Two regions are consistent with clouds of plasma with a temperature of 1 million K about 50 pc in diameter at a distance of 150 pc. These clouds require a particle density of only a factor of 3 above an ambient hot component which may fill a substantial portion of the galactic disk in the vicinity of the sun. Another region near Eridanus is consistent with a low integrated amount of atomic hydrogen along the direction of observation, thereby permitting a greater path length of plasma to contribute to the observed flux. Finally, an extended region in Centaurus shows a temperature of about 20 million K and may be an old supernova remnant expanding into a low-density region of the galactic disk.

Long, K. S.↗