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At least 1,135 records · Page 63
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NASA NTRS1978

Rice University observations of the galactic center

The most sensitive of the four balloon fight observations of the galactic center made by Rice University was conducted in 1974 from Rio Cuarto, Argentina at a float altitude of 4 mbar. The count rate spectrum of the observed background and the energy spectrum of the galactic center region are discussed. The detector used consists of a 6 inch Nal(T 1ambda) central detector collimated to approximately 15 deg FWHM by a Nal(T lamdba) anticoincidence shield. The shield in at least two interaction mean free paths thick at all gamma ray energies. The instrumental resolution is approximately 11% FWHM at 662 keV. Pulses from the central detector are analyzed by two 256 channel PHA's covering the energy range approximately 20 keV to approximately 12 MeV. The detector is equatorially mounted and pointed by command from the ground. Observations are made by measuring source and background alternately for 10 minute periods. Background is measured by rotating the detector 180 deg about the azimuthal axis.

Meegan, C. A.↗
NASA NTRS1978

Future directions in experimental gamma ray astronomy

Better vehicles and instruments are needed if gamma ray spectroscopy in astrophysics and cosmology is to advance. A gamma ray observatory will (1) permit long-term observations of selected sources to measure their variability and to achieve high sensitivity; (2) measure periods in days or weeks; and (3) assess the entire sky to observe various predicted sources, to measure the energy spectrum, and to map the isotropy of the cosmic ray background over larger collecting areas (of the order of a square meter). Conventional and unconventional instruments must cover the energy range from 0.1 MeV to 20 MeV with improved sensitivity. Angular resolution must be improved one degree or more to study discrete X-ray sources in the galactic center. Actively collimated detectors, improved double Compton instruments, and gamma ray correlators to actively synthesize the absolute energy spectrum of the sky protons are discussed as well as the need for scientific balloons.

Haymes, R. C.↗
NASA NTRS1977

Positions of galactic X-ray sources - Galactic latitudes between zero and 20 deg

Precise (to 20 or 25 arcsec) positions of six X-ray sources located in the galactic bulge are reported which were obtained as part of a survey of the galactic plane performed with the SAS-3 rotating modulation collimators. The sources include GX1+4, GX9+9, GX3+1, GX9+1, GX13+1, and GX17+2. The error radii and X-ray intensities (2 to 11 keV) determined for the sources are also presented along with finding charts and proposed optical and radio counterparts. The results are compared with those of previous satellite and sounding-rocket experiments. The status of each source with respect to optical or radio identifications is briefly discussed.

Doxsey, R. E.↗
NASA NTRS1978

Discovery of an X-ray QSO

The discovery of X-ray QSO MR2251-178 at a distance of 410 Mpc is reported. The observations are based on signals (2-11 keV) from NRAO's Very Large Array (VLA) radio telescope and from two independent rotating modulation collimators (RMC). Coordinates are given and positional identification with X-ray source 2A2251-179 is made. Examination of POSS plates and redshift has given rise to speculation that MR2251-178 could actually be a Seyfert galaxy; but its high luminosity would tend to support the contention that it is, indeed, a QSO.

Ricker, G. R.↗
NASA NTRS1978

Observation of X-ray eclipses from LMC X-4

Observations made with the Rotation Modulation Collimator system (RMC) have revealed that X-ray source X-4 in the Large Magellanic Cloud (LMC X-4) is most likely part of a binary system. An analysis of the star's coordinates is presented, with attention given to orbital period and flux intensity variations. Stellar mass and orbital inclination angle are estimated for both X-4 and its companion star.

Li, F.↗
NASA NTRS1978

The X-ray structure of NGC 5128

During an observation of NGC 5128 (Cen A) by the rotating modulation collimator on board the SAS-3 X-ray observatory in early June 1975, data were obtained which suggest the presence of an extended source with about 3 arcmin FWHM surrounding an extremely compact object located at the radio/IR nucleus. The point component exhibited a 25% increase in intensity over a period of 2 to 5 hours.

Delvaille, J. P.↗
NASA NTRS1977

The high-energy celestial X-ray instrument on board OSO-8

The 20 keV-3 MeV celestial X-ray detector on the OSO-8 is described. The primary objectives of this instrument are to measure the energy spectrum of cosmic X-ray sources above 20 keV and to search for time variations, both periodic and irregular, in the intensity of the sources detected. The detector consists of two optically isolated central crystals shielded by a large, active collimator. The sensitive area is 27.5 sq cm and the field-of-view is 5 deg FWHM. The instrument is mounted in the wheel section of OSO-8 with the axis of its field of view offset by 5 deg from the negative spin axis of the wheel. The minimum detectable intensity of a point source which is brought to within 5 deg of the negative spin axis for greater than one day is about 10 to the minus fifth power photons/sq cm-sec at 100 keV.

Dennis, B. R.↗
NASA NTRS1978

The HEAO-B Monitor Proportional Counter Instrument

The Monitor Proportional Counter Instrument for the HEAO-B X-ray Telescope satellite is designed to observe celestial X-ray sources in the range of 1 to 20 keV with intensities exceeding .0002 Crab. It provides both spectral and temporal data, to complement the data from the other HEAO-B instruments, to compare with observations from previous flights, as well as to allow detailed study of time variant X-ray phenomena. The basic detector is a large area proportional counter system, consisting of two counters, high voltage power supplies and preamplifiers, mounted behind a collimator with a 2/3 degree square field of view. The signal processing, power distribution and control electronics are contained in a separate unit, which includes circuitry to perform pulse height analysis, background rejection, time interval measurement, redundancy switching and control, housekeeping and telemetry interfacing.

Gaillardetz, R.↗
NASA NTRS1978

Imaging of X-ray aurorae from Spacelab

The Atmospheric X-ray Emission Telescope (AXET) is designed to image and measure the spatial, temporal, and spectral distributions of X-ray aurorae produced in the upper atmosphere by precipitating energetic electrons. The bremsstrahlung-produced X radiation penetrates to stratospheric depths where it can modify ozone, conductivity, and other critical atmospheric parameters. Remote sensing of this radiation from topside will provide vital data on solar-terrestrial relationships and mechanisms that could help trigger tropospheric response to solar activity. The X rays also provide direct information concerning the dynamics of radiation-belt processes within the magnetosphere. AXET is designed to detect sources up to 50 keV and to image them below 25 keV by means of directionally sensitive proportional counters with passive collimators. It will be mounted in the Space Shuttle on a single fixed platform designed to optimize viewing conditions for the anticipated orbits and aspects of early Spacelab missions.

Goldberg, R. A.↗
NASA NTRS1978

Compact and diffuse X-ray sources in the core of the Perseus cluster /Abell 426/

Data on the X-ray structure of the Perseus cluster of galaxies in the energy range from 2 to 10 keV are analyzed which were obtained during a 12-day observation with the rotating modulation collimator aboard SAS 3. In particular, the nature of the compact X-ray source coincident with NGC 1275 is examined. The data are shown to confirm the presence of a diffuse region of X-ray emission surrounding the nucleus of NGC 1275; it is found that a model which also includes a point source at the nucleus is consistent with the data if the point contribution is no larger than 20% of the X-ray flux detected within 3 to 5 arcmin of the galaxy. The results suggest that NGC 1275 may have accreted a large amount of gas from the intracluster medium and that the flux from the possible point source is consistent with a synchro/Compton model.

Helmken, H.↗
NASA NTRS1978

Nova Ophiuchi 1977 - An X-ray nova

This letter reports the observation by the HEAO 1 satellite experiments of the X-ray nova in Ophiuchus discovered by Kaluzienski and Holt (1977), which is designated H1705-25. The SAO/MIT scanning modulation collimator has been used in conjunction with the NRL large-area sky survey to give two possible positions for the X-ray nova, each having errors of 0.3 by 1.8 arcmin. The discovery of a 16.5-magnitude optical nova (Nova Ophiuchi 1977) in one of the error boxes is reported, and the X-ray source is identified with the optical nova. The object is classified as being of the A0620-00 and A1524-61 type; i.e., a low-mass binary system.

Griffiths, R. E.↗
NASA NTRS1978

Positions of galactic X-ray sources with l/II/ between -20 deg and +6 deg

The precise positions of nine X-ray sources in the vicinity of the galactic center are reported. The data were obtained as part of the comprehensive survey of the galactic plane performed with the rotating modulation collimator detectors on the SAS-3 X-ray observatory. The sources include the binary X-ray source 4U 1700-37 which has a well established optical counterpart that lies 7 sec from the reported position. The other sources GX 349+2, 4U 1702-42, 4U 1705-44, MX 1716-31, A 1742-294, 4U 1755-33, GX 5-1, and 2S 1803-245 lack established counterparts in other wavelengths. The obtained position for GX 5-1 adds confidence to the radio counterpart proposed by Braes et al. (1972). The reported position for 4U 1755-33 excludes the optical counterpart proposed by Jones et al. (1974).

Jernigan, J. G.↗
NASA NTRS1978

Thirty-centimeter-diameter ion milling source

A 30-cm beam diameter ion source has been designed and fabricated for micromachining and sputtering applications. An argon ion current density of 1 mA/cu cm at 500 eV ion energy was selected as a design operating condition. The completed ion source met the design criteria at this operating condition with a uniform and well-collimated beam having an average variation in current density of + or - 5% over the center of 20 cm of the beam. This ion source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. Langmuir probe surveys of the source plasma support the design concepts of a multipole field and a circumferential cathode to enhance plasma uniformity.

Robinson, R. S.↗
NASA NTRS1978

Discovery of 3.6-s X-ray pulsations from 4U0115+63

SAS 3 observations reveal a pulsation period of 3.61 sec for the transient X-ray source 4U0115+63. Positional measurement is accurate to approximately 30 arc s, and has led to the likely identification of an optical counterpart. The intensity of the pulses, as reported on 5.9 January 1978, is given as approximately 1.7 times that of the Crab Nebula (1-27 keV). Spectral information was also obtained from the ratios of counting rates in the first three energy channels of the center slat collimator detector (1-27 keV). Two classes of models are proposed to explain the transient nature of the X-ray sources: (1) episodic mass transfer in a binary system, and (2) eccentric binary orbits.

Cominsky, L.↗
NASA NTRS1978

X-ray and radio emission from the compact galaxy III Zw 2

X-rays from the compact galaxy III Zw 2 have been detected with the rotating modulation collimator on board SAS 3. The (2-10-keV) flux is (4.3 + or - 0.5) by 10 to the -11th power erg/sq cm per sec, which corresponds to a luminosity of 1.4 by 10 to the 45th power erg/s at 530 Mpc. Subsequent radio observations between 1.46 and 90 GHz were made at the NRAO Very Large Array and 36-foot (11-m) installations. The radio spectrum rises sharply toward higher frequencies and, below about 100 GHz, is indicative of a self-absorbed synchrotron spectrum from an extremely compact, rapidly evolving object.

Schnopper, H. W.↗
NASA NTRS1978

High-resolution observations of X-ray sources at the galactic center

A region about 1 deg of arc in radius and centered on the galactic nucleus has been surveyed during a rocket flight, using X-ray detectors equipped with 10-arcmin by 4-deg (FWHM) collimators. The extended source 4U 1743-29 has been resolved into at least four discrete sources having luminosities (2-10 KeV) between 4 by 10 to the 36th power and 3.5 by 10 to the 37th power erg/s.

Cruddace, R. G.↗
NASA NTRS1977

Design, fabrication and performance of two grazing incidence telescopes for celestial extreme ultraviolet astronomy

The design and performance of grazing incidence telescopes for celestial extreme ultraviolet (EUV) astronomy are described. The telescopes basically consist of a star tracker, collimator, grazing incidence mirror, vacuum box lid, vacuum housing, filters, a ranicon detector, an electronics box, and an aspect camera. For the survey mirror a Wolter-Schwarzschild type II configuration was selected. Diamond-turning was used for mirror fabrication, a technique which machines surfaces to the order of 10 microns over the required dimensions. The design of the EUV spectrometer is discussed with particular reference to the optics for a primarily spectroscopic application and the fabrication of the f/10 optics.

Lampton, M.↗
NASA NTRS1978

Position and pulse profile of the X-ray transient 4U 0115 + 63

The celestial position of the 3.6-s X-ray pulsar, 4U 0115 + 63, has been measured to a precision of 12 arcsec in one dimension with the scanning modulation collimator experiment on HEAO 1. This result, together with a position obtained with SAS 3, has led to the identification of an early-type star as the optical counterpart. An X-ray luminosity of approximately 3 by 10 to the 37th power erg/s (3-13 keV) is inferred from the observed flux of about 30% that of the Crab and an estimated distance of 5 kpc. The pulse profile over the energy range 3-13 keV is similar to that of Cen X-3.

Johnston, M.↗