Engineering topics

Priedhorsky, W.

Publications and source records attributed to Priedhorsky, W..

9 records

NASA NTRS1990

Highly curved microchannel plates

Several spherically curved microchannel plate (MCP) stack configurations were studied as part of an ongoing astrophysical detector development program, and as part of the development of the ALEXIS satellite payload. MCP pairs with surface radii of curvature as small as 7 cm, and diameters up to 46 mm have been evaluated. The experiments show that the gain (greater than 1.5 x 10 exp 7) and background characteristics (about 0.5 events/sq cm per sec) of highly curved MCP stacks are in general equivalent to the performance achieved with flat MCP stacks of similar configuration. However, gain variations across the curved MCP's due to variations in the channel length to diameter ratio are observed. The overall pulse height distribution of a highly curved surface MCP stack (greater than 50 percent FWHM) is thus broader than its flat counterpart (less than 30 percent). Preconditioning of curved MCP stacks gives comparable results to flat MCP stacks, but it also decreases the overall gain variations. Flat fields of curved MCP stacks have the same general characteristics as flat MCP stacks.

Siegmund, O. H. W.↗

NASA NTRS1989

MOXE: An X-ray all-sky monitor for Soviet Spectrum-X-Gamma Mission

A Monitoring Monitoring X-Ray Equipment (MOXE) is being developed for the Soviet Spectrum-X-Gamma Mission. MOXE is an X-ray all-sky monitor based on array of pinhole cameras, to be provided via a collaboration between Goddard Space Flight Center and Los Alamos National Laboratory. The objectives are to alert other observers on Spectrum-X-Gamma and other platforms of interesting transient activity, and to synoptically monitor the X-ray sky and study long-term changes in X-ray binaries. MOXE will be sensitive to sources as faint as 2 milliCrab (5 sigma) in 1 day, and cover the 2 to 20 KeV band.

Priedhorsky, W.↗

NASA NTRS1989

MOXE - An X-ray all-sky monitor for the Soviet Spectrum-X-Gamma mission

A Monitoring X-Ray Equipment (MOXE) is being developed for the Soviet Spectrum-X-Gamma Mission. MOXE is an X-ray all-sky monitor based on array of pinhole cameras, to be provided via a collaboration between Goddard Space Flight Center and Los Alamos National Laboratory. The objectives are to alert other observers on Spectrum-X-Gamma and other platforms of interesting transient activity, and to synoptically monitor the X-ray sky and study long-term changes in X-ray binaries. MOXE will be sensitive to source as faint as 2 milliCrab (5 sigma) in 1 day, and cover the 2 to 20 KeV band.

Priedhorsky, W.↗

NASA NTRS1987

Disappearance of periodic X-ray minima in AM Her

Optical, soft X-ray, and medium energy X-ray measurements taken during an unusual high state of AM Her are reported. The X-ray and secondary optical minima disappeared from the light curve. The X-ray flux varied perodically. In each X-ray band, the flux during the expected phase of minimum was approximately the same as the average during the rest of the cycle. The optical and medium energy X-ray fluxes were at all-time highs; however, the soft X-ray flux was low by a factor of 3 compared to the nominal high state. This change in the ratio of medium to soft X-ray flux is difficult to fit into the standard scenario for AM Her, where soft X-rays are interpreted as reprocessed optical and medium energy X-ray flux. The peculiar light curve of AM Her was probably caused by a small shift in the position of the accretion column with respect to the rotation axis, so that the normal grazing eclipse of the accretion column did not take place.

Priedhorsky, W.↗

NASA NTRS1986

Bimodal quasi-oscillatory and spectral behavior in Scorpius X-1

Exosat observations of Sco X-1 obtained using the Xe and/or Ar detectors for a total of about 80,000 s during four runs on August 24-27, 1985 are reported and analyzed. Two modes of quasi-periodic oscillations (QPOs) corresponding to the quiescent and active states of Sco X-1 and to two modes of spectral behavior are identified and characterized, confirming the findings of Priedhorsky (1985) and Middleditch and Priedhorsky (1986). In the quiescent state, the QPO frequency is about 6 Hz and is anticorrelated with intensity, and the spectral hardness ratio (14-21 vs 2-7 keV) varies steeply with intensity; in the active state, QPO frequency is correlated with intensity and varies from 10 to 20 Hz, and the spectral-hardness-ratio/intensity curve is flatter. Previous observations of bimodal behavior in other bands are summarized, and theoretical models proposed to explain them are discussed.

Priedhorsky, W.↗

NASA NTRS1986

Disappearance of periodic X-ray minima in AM Her

Optical, soft X-ray, and medium energy X-ray measurements taken during an unusual high state of AM Her are reported. The X-ray and secondary optical minima disappeared from the light curve. The X-ray flux varied periodically. In each X-ray band, the flux during the expected phase of minimum was approximately the same as the average during the rest of the cycle. The optical and medium energy X-ray fluxes were at all-time highs; however, the soft X-ray flux was low by a factor of 3 compared to the nominal high state. This change in the ratio of medium to soft X-ray flux is difficult to fit into the standard scenario for AM Her, where soft X-rays are interpreted as reprocessed optical and medium energy X-ray flux. The peculiar light curve of AM Her was probably caused by a small shift in the position of the accretion column with respect to the rotation axis, so that the normal grazing eclipse of the accretion column did not take place.

Priedhorsky, W.↗

NASA NTRS1985

Bimodal quasi-oscillatory and spectral behavior in Sco X-1

X-ray observations were made to follow up the discovery of quasi-periodic oscillations (QPO) in Sco X-1. The QPO is observed in the quiescent state, and between flares in the active state. When the source is quiescent, the QPO frequency is 6 Hz and anticorrelated with intensity; in the active state, the frequency ranges from 10 to 20 Hz and is strongly correlated with intensity. At high intensities the QPO dissolves into continuum noise. The QPO rms amplitude decreases with count rate, and increases with photon energy. There are two modes of spectral behavior, with a one-to-one correspondence to the two modes of QPO: the spectral hardness ratio varies more steeply with intensity when the source shows 6 Hz QPO, than for 10 to 20 Hz QPO. Transitions between QPO modes, which occur when the flux is at its lowest levels, correspond to transitions between hardness ratio modes. The QPO frequency changes continuously through the transitions, which last a few hundred seconds.

Priedhorsky, W.↗

NASA NTRS1979

Extended-bandwidth X-ray observations of Cygnus X-1

An energy- and time-resolved observation of Cyg X-1, sensitive from 0.15 to 20 keV, is reported which was performed to investigate the spectrum and time variability of the flux at low X-ray energies. Data in the band from 1.5 to 42 keV, obtained in two previous rocket flights, are reanalyzed to search for any energy dependence of the time signature. No such energy dependence is found, so the explanation of the observed low-energy excess of Cyg X-1 as emission from an extended region separate from the high-energy source is rendered untenable. The evident stability of the power-law spectrum of Cyg X-1 through the observed shot-noise variation is shown to suggest that the spectrum has a Comptonization origin. It is concluded that there is no obvious analogy to be made between Cyg X-1 and X-ray bursters.

Priedhorsky, W.↗

NASA NTRS1978

Joint infrared and visual monitoring of AM Herculis

Four cycles of the flux from the 3.1 hour X-ray variable AM Her have been observed simultaneously at four wavelengths in the visible and near-infrared. The data show periodic variations at all wavelengths but show systematic changes with wavelength in the relative depths and widths of the primary and secondary minima. The spectral energy distribution varies with phase, being reddest at primary minimum and bluest at the maximum. At primary minimum it is consistent with the energy distribution of an M2 V star plus a component which is flat with frequency; if an M2 V star is present, a lower limit of 100 pc can be placed on the distance to AM Her. The implications of the data on several models for AM Her are discussed.

Priedhorsky, W.↗