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At least 811 records · Page 45
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NASA NTRS1986

A Fourier transform telescope for sub-arcsecond imaging of X-rays and gamma rays

This paper describes a Fourier transform telescope designed to image solar flare X-rays and gamma rays at energies up to 1 MeV with arcsec resolution. The imaging technique makes use of a bigrid collimator divided into a number of smaller areas called subcollimators. The grids in each subcollimator consist of a set of linear apertures so configured that each subcollimator provides a measurement of a single Fourier component of the angular distribution of the source. The imaging concept is therefore a mathematical analog to aperture synthesis in radio astronomy. For X-ray and gamma-ray astronomy, this approach has significant advantages in terms of relaxed requirements for astronomy, this approach has significant advantages in terms of relaxed requirements for position sensitivity in the detector and for control of grid alignment in the large scale telescope structure. The concept of the Fourier transform telescope will be illustrated with numerical parameters of a version now under study for the Pinhole/Occulter Facility.

Crannell, C. J.↗
NASA NTRS1988

A high-resolution gamma-ray and hard X-ray spectrometer for solar flare observations in Max 1991

A long duration balloon flight instrument for Max 1991 designed to study the acceleration of greater than 10 MeV ions and greater than 15 keV electrons in solar flares through high resolution spectroscopy of the gamma ray lines and hard X-ray and gamma ray continuum is described. The instrument, HIREGS, consists of an array of high-purity, n-type coaxial germanium detectors (HPGe) cooled to less than 90 K and surrounded by a bismuth germanate (BGO) anticoincidence shield. It will cover the energy range 15 keV to 20 MeV with keV spectral resolution, sufficient for accurate measurement of all parameters of the expected gamma ray lines with the exception of the neutron capture deuterium line. Electrical segmentation of the HPGe detector into a thin front segment and a thick rear segment, together with pulse-shape discrimination, provides optimal dynamic range and signal-to-background characteristics for flare measurements. Neutrons and gamma rays up to approximately 0.1 to 1 GeV can be detected and identified with the combination of the HPGe detectors and rear BGO shield. The HIREGS is planned for long duration balloon flights (LDBF) for solar flare studies during Max 1991. The two exploratory LDBFs carried out at mid-latitudes in 1987 to 1988 are described, and the LDBFs in Antarctica, which could in principle provide 24 hour/day solar coverage and very long flight durations (20 to 30 days) because of minimal ballast requirements are discussed.

Lin, R. P.↗
NASA NTRS1988

Gamma-ray and hard X-ray imaging of solar flares

The scientific and technical aspects of high-resolution gamma-ray and X-ray imaging of solar flares are discussed. The scientific necessity for imaging observations of solar flares and the implications of future observations for the study of solar flare electrons and ions are considered. Performance parameters for a future hard X-ray and gamma-ray imager are summarized. Techniques for high-energy photon imaging including direct collimation imaging, coded apertures, and modulation collimators are surveyed. The technique of Fourier-transform imaging is examined. The options for detectors and grid fabrication are reviewed. Several planned future high-energy imagers are described.

Prince, T. A.↗
NASA NTRS1988

High energy gamma-ray observations of SN 1987A

Results are presented from observations of SN 1987A made with a combined high energy gamma ray and hard X-ray payload carried on a balloon flight over Alice Springs, Australia on April 5, 1988. The payload instrumentation is described, emphasizing the characteristics of the gamma-ray detector. The gamma-ray emission profile is illustrated and the preliminary results of the observations are summarized.

Sood, R. K.↗
NASA NTRS1989

Einstein SSS and MPC observations of Aql X-1 and 4U1820-30

The results of timing and spectral analyses of the X-ray sources Aql X-1 (X1908+005) and 4U1820-30 (NGC6624) are reported using data obtained with the Einstein SSS (Solid State Spectrometer) and MPC (Monitor Proportional Counter) instruments. A classic type I burst was observed from Aql X-1 in both detectors and a coherent modulation with a period of 131.66 + or - 0.02 ms and a pulsed fraction of 10 percent was detected in the SSS data. There is no evidence for a loss of coherance during the approximately 80 sec when the burst is observable. The 2 sigma upper limit on the rate of change of the pulse period is 0.00005s/s. It is argued that an asymmetrical burst occurring on a neutron star rotating at 7.6 Hz offers a plausible explanation for the oscillation. The data from 4U1820-30 show that the amplitude of the 685 sec modulation, identified as the orbital period, is independent of energy down to 0.6 keV. The SSS data show that the light curve in the 0.6 to 4.5 keV band is smoother than at higher energies.

Kelley, R. L.↗
NASA NTRS1989

Search for soft X-ray emission from SN 1987A with a CCD X-ray imaging spectrometer

The results of soft X-ray observations of SN 1987A over the energy band 0.65-2.0 keV are reported. The upper limits on the soft X-ray flux are inconsistent with an extrapolation of the spectrum measured by the Ginga Satellite to the energy band and require a turnover in the X-ray spectrum between 2 and 4 keV. If this turnover is due to absorption by intervening material, a neutral column density associated with the supernova of at least 2.8 x 10 to the 21st/sq cm is required. The background rate for the Texas Instruments 800 x 800 pixel CCD, measured between 150 and 285 km altitude, was 1.1 counts/sq cm s. The background spectrum has a broad peak at 350 electrons, corresponding to charge deposited in the detector by minimally ionizing particles.

Burrows, D. N.↗
NASA NTRS1989

Performance of the large-area detectors for the Burst and Transient Source Experiment (BATSE) on the Gamma Ray Observatory

BATSE, one of four experiments on the Gamma Ray Observatory (GRO), is expected to provide the most sensitive observations of gamma-ray bursts yet obtained, as well as to provide long-term monitoring of hard X-ray and low-energy gamma-ray emission from bright pulsating sources, transients, and solar flares. Eight uncollimated modules, positioned at the corners of the spacecraft to provide an unobstructed view of the sky, detect sources by various techniques based on time variability. Use of detectors with anisotropic response allows location of gamma-ray bursts to be determined to an accuracy of about 1 deg using BATSE data alone. The completed BATSE underwent intensive testing and calibration prior to its delivery in October 1988.

Paciesas, W. S.↗
NASA NTRS1991

Detection of coherent 7.6 Hz oscillations during a burst from Aquila X-1

The results are reported of timing and spectral analysis of the X-ray source Aql X-1 (X1908 + 005) using data obtained with the Einstein SSS and MPC instruments. A classic type I burst was observed from Aql X-1 in both detectors, and a coherent modulation with a period of 131.66 + or - 0.02 (7.6 Hz) and a pulsed fraction of 10 percent was detected in the SSS data (0.64-4.5 keV) during the period of enhanced emission. The signal has a random occurrence probability of less than 5 x 10 to the -5th. The sensitivity of the MPC for high-resolution timing during the burst is greatly reduced because of the low-duty cycle during the burst, and the modulation is not detected. There is no evidence for a loss of coherence during the 80 s or so when it is observable. It is argued that an asymmetrical burst occurring on a neutron star rotating at 7.6 Hz offers a plausible explanation for the oscillation.

Schoelkopf, R. J.↗
NASA NTRS1990

High-revolution gamma-ray imaging from the moon

An observatory is suggested for exploiting unique lunar features to perform sensitive, subarcsecond cosmic X-ray and gamma-ray imaging. The observatory would be built in an evolutionary manner and would eventually include several different position-sensitive detector systems which together would cover a broad energy range and address a wide variety of astrophysical problems. High angular resolution would be obtained by using a mobile crane on the flat lunar mare regions to move a coded aperture mask for source tracking with detector/mask separations of up to 5 kilometers.

Mahoney, William A.↗
NASA NTRS1992

The solar X-ray/cosmic gamma-ray burst experiment aboard Ulysses

The scientific objectives of the Ulysses solar X-ray/cosmic gamma-ray burst experiment, and the unique features of the Ulysses mission which will help to achieve them are described. After a discussion of the special design constraints imposed by the mission, the sensor systems, consisting of two CsI scintillators and two Si surface barrier detectors covering the energy range 5-150 keV are described. Their operating modes and inflight performance are also given.

Hurley, K.↗
NASA NTRS1991

High energy neutrinos from primary cosmic rays accelerated in the cores of active galaxies

The spectra and high-energy neutrino fluxes are calculated from photomeson production in active galactic nuclei (AGN) such as quasars and Seyfert galaxies using recent UV and X-ray observations to define the photon fields and an accretion-disk shock-acceleration model for producing ultrahigh-energy cosmic rays in the AGN. Collectively AGN should produce the dominant isotropic neutrino background between 10 exp 4 and 10 exp 10 GeV. Measurement of this background could be critical in determining the energy-generation mechanism, evolution, and distribution of AGN. High-energy background spectra and spectra from bright AGN such as NGC4151 and 3C273 are predicted which should be observable with present detectors. High energy AGN nus should produce a sphere of stellar disruption around their cores which could explain their observed broad-line emission regions.

Stecker, F. W.↗
NASA NTRS1990

Design criteria for small coded aperture masks in gamma-ray astronomy

Most theoretical work on coded aperture masks in X-ray and low-energy gamma-ray astronomy has concentrated on masks with large numbers of elements. For gamma-ray spectrometers in the MeV range, the detector plane usually has only a few discrete elements, so that masks with small numbers of elements are called for. For this case it is feasible to analyze by computer all the possible mask patterns of given dimension to find the ones that best satisfy the desired performance criteria. A particular set of performance criteria for comparing the flux sensitivities, source positioning accuracies and transparencies of different mask patterns is developed. The results of such a computer analysis for masks up to dimension 5 x 5 unit cell are presented and it is concluded that there is a great deal of flexibility in the choice of mask pattern for each dimension.

Sembay, S.↗
NASA NTRS1992

Correlated optical observations with BATSE/CGRO on SCO X-1

The Burst and Transient Source Experiment (BATSE) instrument on the Compton Gamma-Ray Observatory consists of two banks of eight instruments referred to as the Large Area Detectors (LADs) and the Spectroscopic Detectors (SDs). Each LAD crystal is 50.8 cm in diameter by 1.27 cm thick while for a SD these values are 12.7 cm in diameter by 7.62 cm in diameter. Both the LADs and SDs are NaI(TI) scintillation detectors. The LADs and SDs are situated on the CGRO spacecraft so as to provide all sky coverage for both sets of detectors. The SDs have the ability to measure energies in the 8-16 keV range whereas the minimum energy at which the LADs operate is near 20 keV. SCO X-1 is the brightest continuous x-ray source in the sky. It is believed to consist of a low mass star orbiting and transferring mass onto a neutron star. It is representative of a class of similar objects referred to as low mass x-ray binaries (LMXB). Because SCO X-1 serves as the prototype of this class of x-ray emitters and since its detectable emission is so large, it warrants extended study. One of the most fruitful techniques of studying a LMXB system is by simultaneously monitoring its emission at a variety of different wavelengths. These correlated datasets can be used to probe the source environment, investigate emission mechanisms, and examine the mass transfer process itself. In principle, the BATSE SDs have the capability of providing a nearly continuous 8-16 keV record of SCO X-1 activity. The aim of this study was to investigate the feasibility of using the BATSE SDs along with simultaneous optical measurements to study this source.

Mcnamara, Bernard↗
NASA NTRS1992

The Ulysses solar X-ray/cosmic gamma-ray burst experiment

The Ulysses X-ray and gamma-ray instrument is described, and its scientific objectives are presented. Some aspects of the history of the Ulysses mission are explained, as well as of the design considerations for this experiment. As this mission will be the most distant one from earth ever to carry a burst detector, the primary cosmic objective will be to localize gamma-burst sources by triangulation.

Hurley, Kevin↗
NASA NTRS1992

Performances of the Imaging Proportional Counter of the Stellar X-ray Polarimeter

The Stellar X-ray Polarimeter (SXRP) will be mounted on the focal plane of one of the two SODART telescopes aboard the Russian mission Spectrum-X-gamma. The SXRP employs the same Imaging Proportional Counters for both the Bragg and the scattering stages. An account is presently given of the main characteristics of these detectors and their performance, on the basis of tests at the technical-model and engineering model levels of development.

Costa, E.↗
NASA NTRS1992

Gamma-ray astronomy using a high pressure gas scintillation drift chamber with a waveshifting fiber readout

We describe a balloon-borne hard X-ray telescope called SIGHT (Scintillation Imaging Gas-filled Hard X-ray Telescope). SIGHT is a high sensitivity, good energy resolution instrument that images in the 30 to 300 keV region. We discuss the development of a large area, 20 atmosphere, position sensitive xenon gas scintillation drift chamber which is the gamma-ray detector at the heart of the telescope package. Results of the development of the novel waveshifting fiber readout for this chamber are presented.

Wilkerson, J.↗
NASA NTRS1992

Development of hard X-ray optics

Studies of cosmic X-ray sources have suffered from lack of focussing optics in the hard X-ray spectral region (E above 10 keV); in the absence of imaging optics, celestial X-rays are masked by the cosmic ray background, which severely degrades the detector sensitivity. There are several possible ways to develop grazing incidence imaging optics for this spectral region; we describe here one approach which utilizes numerous large diameter silicon wafers to form a flat-plate imaging telescope. A prototype imager of this type has been constructed, and we present measurements of surface quality, coalignment accuracy, and imaging ability.

Joy, Marshall↗
NASA NTRS1992

The Germanium GAlactic Plane Patrol mission

The goal of the Germanium GAlactic Plane Patrol mission (GGAPP) is to provide a continuous monitor of the Galactic Plane (GP) for variable sources of gamma-ray lines. Potentially interesting sources include black hole candidates, X-ray binary systems, pulsars, gamma-ray bursts, and solar flares. The GGAPP instrument is an array of Ge detectors cooled by a mechanical refrigerator to achieve a spectral resolution of 2 keV at 1 MeV (1/500). A bismuth germanate (BGO) shield will restrict the field-of-view (FOV) to within 20 deg of the GP, and a modulation collimator system will locate strong sources to less than 0.3 deg in galactic longitude, provide a direct means of subtracting background, and mapping the diffuse emission from the GP. The spacecraft will be rotationally stabilized with the spin axis perpendicular to the GP such that the modulator scans in galactic longitude. A HEO or L1 orbit will keep GGAPP far away from the strong background produced by the Earth. GGAPP will provide a natural bridge between GRO and future missions such as INTEGRAL/NAE.

Tueller, Jack↗