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Garmire, G. P.

Publications and source records attributed to Garmire, G. P..

At least 55 records · Page 3
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NASA NTRS1979

Soft X-ray emission from the vicinity of the dwarf nova AY Lyrae

The detection of a low-intensity soft X-ray source in the region of the dwarf nova AY Lyrae is reported. The source, designated H1839 plus 37, appeared in superpositions of HEAO A2 X-ray scans taken on October 9, 1977; it was observed only in the energy interval 0.18 to 0.43 keV. The peak intensity was 0.014 plus or minus 0.0027 counts/sq cm/sec. If a thermal bremsstrahlung spectrum is assumed, the estimated upper temperature limit of the source is 5 million K; an upper limit of 1.4 million K is implied if a black-body fit is assumed.

Cordova, F. A.↗
NASA NTRS1979

Discovery of X-ray emission from two southern supernova remnants

Two soft X-ray sources positionally coincident with the supernova remnants PKS 1209-52 and RCW 103 have been discovered by using the A-2 experiment on HEAO 1. Their measured fluxes are, respectively, about 1.4 x 10 to the -10th erg/cm-sec (0.2-1.0 keV) and about 1.8 x 10 to the -10th erg/cm-sec (0.6-2.0 keV). Spectral data are used to derive physical parameters for each remnant. For PKS 1209-52 the parameters are suggestive of the remnant's being in an advanced evolutionary phase, with shock-heated interstellar material producing the soft X-ray emission. RCW 103, in contrast, is known from radio and optical data to be in an earlier evolutionary phase, and the soft X-ray flux is most likely due to emission originating in a reflected shock wave or in plasma evaporated from shock-heated interstellar clouds.

Tuohy, I. R.↗
NASA NTRS1979

Evidence for X-ray emission from Kepler's supernova remnant

Evidence for weak soft X-ray emission from the remnant of Kepler's supernova has been acquired by the low energy detectors of the A 2 experiment on HEAO 1. A soft X-ray source has been detected using a narrow field of view sensitive to X rays between 0.2 and 3 keV and is found to be the only constant X-ray source within the error box containing Kepler's supernova remnant. The intensity of the X-ray source is calculated to be about 6.3 x 10 to the -2 counts/sq cm sec, with an intrinsic X-ray luminosity in the energy range 0.3 to 3 keV of about 28 x 10 to the 35 erg/sec if, as is widely believed, the remnant is at a distance of 4 kpc. Observations from HEAO 2 will allow the detection to be confirmed, the source to be imaged and its spectrum to be determined.

Tuohy, I. R.↗
NASA NTRS1979

A search for X-ray pulsations from the Galactic Centre

A search has been conducted for periodic X-ray behavior in the Galactic Center, a region known to contain several point sources. No pulsations are detected in the range from about 2 sec to 2000 sec. The assumption that part of the steady flux from the Galactic Center is due to the steady contribution of bursters is discussed. It is also noted that the absence of pulsations does not necessarily undermine the proposed binary-neutron star models for the burst sources.

Cordova, F. A.↗
NASA NTRS1979

Low luminosity galactic X-ray sources

The number of low luminosity sources found in the Galaxy has increased from a few to more than two dozen in the past three years. The sources range from isolated hot white dwarfs (HZ43) to normal stellar coronae (alpha Cen), very active coronal stars (RS CVn), flare stars (UV Ceti), interacting winds and stellar surfaces (Algol), and finally to accretion onto white dwarfs (AM Her, steady; U Gem, impulsive). The following review discusses each of these classes in some detail and portrays the wide variety of physical phenomena leading to X-ray emission.

Garmire, G. P.↗
NASA NTRS1979

HEAO-1 observations of AM Herculis between 0.1 and 3 keV

Results are reported for HEAO A2 scanning observations of AM Her in the energy range from 0.1 to 3 keV. A light curve of AM Her is plotted, a typical flux of 8 x 10 to the -10th erg/sq cm-sec in the 0.15-0.5-keV range at X-ray maximum is estimated, and no pronounced spectral variation with phase is detected. It is found that both a 0.025-keV blackbody spectrum and an exponential spectrum with an energy-dependent Gaunt factor provide an acceptable fit to the data. It is concluded that the spectrum of the radiation from the plasma at the surface of the strongly magnetic and relatively massive white dwarf in AM Her consists of three components: (1) a high-temperature (about 100 million to 1 billion K) component produced by electron-ion bremsstrahlung in the hot postshock plasma; (2) a blackbody component of about 100,000 to 1 million K produced by the heated surface of the white dwarf; and (3) a still softer component produced by optically thick electron cyclotron emission in the postshock region.

Tuohy, I. R.↗
NASA NTRS1979

Experiments with diamond-turned metal X-ray mirrors

It is noted that the primary advantages of diamond turning technology for the fabrication of X-ray telescope mirrors is in the smoothness of the finished surface and the control of the position of the cutter afforded by the precision slides and computer-assisted positioners which form the surface. The paper summarizes the Caltech work in attempting to make Wolter Type I telescope mirrors using the diamond turning facilities at the Oak Ridge Y-12 laboratory. Attention is given to such factors as the use of aluminum with copper plating and electroless nickel coating. It is found that although the diamond turning capability of the Y-12 lab is capable of making good X-ray mirror contours, there are problems in the process which have limited the accuracy achieved by this technique.

Garmire, G. P.↗
NASA NTRS1978

New evidence on the nature of the soft X-ray source in AM Herculis from HEAO 1

Results are reported for scanning observations of AM Herculis from HEAO 1 during the period September 22-October 12, 1977. The soft X-ray light curve constructed from the observations shows considerable scatter in intensity, together with clear evidence for a residual flux during X-ray minimum. At X-ray maximum the flux in the energy range 0.15-0.5 keV is typically 8 x 10 to the -10th power erg/sq cm per sec. The spectrum of AM Her is characterized by a sharp turnover at 0.2 keV and is well described by a blackbody model with absorption. There is no appreciable change in the spectrum with binary phase. The present observations, when combined with theoretical models, imply that the soft X-rays are produced by the heated surface of the degenerate dwarf component, and that the surface has a temperature of approximately 400,000 K and a luminosity about 30 times that observed at optical or hard X-ray wavelengths. AM Her is predicted to be a spectacular UV source, with an intrinsic UV luminosity comparable to that in soft X-rays.

Tuohy, I. R.↗
NASA NTRS1978

A search for X-ray pulsations from the galactic center

Data from the SAS-3 satellite were used in a search for X-ray pulsations from the direction of the galactic center. No periodic X-ray behavior was detected in the frequency interval 0.6 Hz to 0.0006 Hz and energy range 2.5 - 35 keV. For periods less than 60 sec, the upper limit to the amplitude of any pulsation in the 2.5 - 10 keV band is approximately .0017 cts/sq cm/s. This corresponds to a pulsed fraction of approximately 1.3 percent of the total GCX flux. Somewhat higher limits apply for longer periods and for energies greater than 10 keV.

Cordova, F. A.↗
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.↗
NASA NTRS1976

Soft X-rays from the Large Magellanic Cloud - Implications on the origin of the diffuse X-ray background

A total soft X-ray luminosity of approximately 10 to the 38th power ergs/s was observed from the Large Magellanic Cloud (LMC) during pointed rocket observations in November 1973. Simple spectral parameters are derived and discussed. Upper limits at 1 KeV to several known LMC point sources are presented. A diffuse bar source reported previously was not detected. Strong limits are placed on the fraction of halo and extragalactic diffuse X-ray flux observed in the direction of the LMC due to the lack of correlation of the 0.25-KeV diffuse flux with interstellar hydrogen in the Galaxy and in the LMC.

Long, K. S.↗
NASA NTRS1976

X-ray spectra of the Puppis A and the Vela supernova remnants

Low-energy X-ray spectra are presented for the entire Vela supernova remnant (SNR), the two most intense subregions of the Vela SNR, and the Puppis A SNR. Acceptable chi-squared fits are obtained from the model of a high-temperature low-density plasma with Allen cosmic abundances when thermal bremsstrahlung, radiative recombination, line emission, and interstellar absorption are included. A suggested increase of 45-fold in the Si abundance for the entire Vela SNR is found unacceptable by chi-squared tests of the present spectra. The two enhanced regions of Vela are found to have different temperatures. A deficiency of at least a factor of 3 is seen in the O VII and O VIII emission from the entire Vela SNR. Because ultraviolet observations indicate a normal abundance of oxygen, this is interpreted as evidence for the existence of nonequilibrium conditions in the emitting plasma.

Moore, W. E.↗
NASA NTRS1976

Support of selected X-ray studies to be performed using data from the Uhuru (SAS-A) satellite

A new measurement of the diffuse X-ray emission sets more stringent upper limits on the fluctuations of the background and on the number counts of X-ray sources with absolute value of b 20 deg than previous measurements. A random sample of background data from the Uhuru satellite gives a relative fluctuation in excess of statistics of 2.0% between 2.4 and 6.9 keV. The hypothesis that the relative fluctuation exceeds 2.9% can be rejected at the 90% confidence level. No discernable energy dependence is evident in the fluctuations in the pulse height data, when separated into three energy channels of nearly equal width from 1.8 to 10.0 keV. The probability distribution of fluctuations was convolved with the photon noise and cosmic ray background deviation (obtained from the earth-viewing data) to yield the differential source count distribution for high latitude sources. Results imply that a maximum of 160 sources could be between 1.7 and 5.1 x 10 to the -11 power ergs/sq cm/sec (1-3 Uhuru counts).

Garmire, G. P.↗
NASA NTRS1976

X-ray astronomy program at CIT

The X-ray astronomy program includes a rocket-borne Wolter type 1 telescope with associated position sensitive detectors, ground based observations in the optical and infrared spectral bands, an experiment on the HEAO-A spacecraft, and a rocket-borne test flight of the HEAO-A. A modified detector was used to study Cyg X-1 millisecond pulse structure and spectra.

Garmire, G. P.↗
NASA NTRS1975

Search for extreme ultraviolet radiation from selected stars

Results are reported for a search for EUV radiation between 140 and 430 A from selected objects which was conducted with a rocket-borne EUV filter photometer. The candidate objects included the bright planetary nebula NGC 2392 and the stars gamma Gem, alpha CMa, omicron-prime CMa, and gamma-2 Vel. Upper limits (2-sigma level) to the flux near 200 A are determined for the five objects, and estimates of the expected 200-A helium-continuum flux are derived for two of the stars on the basis of the hot-corona model. It is found that the calculated upper limits are at least two orders of magnitude higher than plausible flux estimates based on the hot-corona model. However, it is noted that uncertainties in the flux estimates are great enough to make the upper limits useful.

Riegler, G. R.↗
NASA NTRS1974

High angular resolution cosmic X-ray astronomy observations in the energy range 0.15-2 keV and XUV observations of nearby stars from an attitude controlled rocket

The construction of a two dimensional focusing Wolter Type I mirror system for X-ray and XUV astronomical observations from an Astrobee F sounding rocket is described. The mirror design goal will have a one degree field, a 20-arc seconds resolution, an effective area of about 50 sq cm at 1 keV and 10 sq cm at 0.25 keV on axis. A star camera provides aspect data to about 15-arc seconds. Two detectors are placed at the focus with an interchange mechanism to allow a detector change during flight. The following specific developments are reported: (1) position sensitive proportional counter development; (2) channel plate multiplier development; (3) telescope mirror development and payload structure; (4) Australian rocket flight results; (5) Comet Kohoutek He I observation; and (6) Vela, Puppis A, and Gem-Mon bright patch observations.

Garmire, G. P.↗
NASA NTRS1974

Observation of soft X-ray emission from a region near Per X-1

Soft X-ray emission from the X-ray source Per X-1 was observed in the 0.4-2 keV energy interval from a rocket-borne X-ray detector. Spectral analysis of the data indicates that in the 0.4-2 keV band the X-ray emission from Per X-1 can be fitted either with a power law or a steep thermal bremsstrahlung spectrum. This steep spectrum is inconsistent with the spectrum measured above 2 keV. The measured flux in 0.4-2 keV band corresponds to X-ray luminosity of 3 times 10 to the 45th ergs per second for Per X-1.

Agrawal, P. C.↗