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The progress made during 1995 on the Monte-Carlo gamma-ray spectrum simulation program BSIMUL is discussed. Several features have been added, including the ability to model shields that are tapered cylinders. Several simulations were made on the Near Earth Asteroid Rendezvous detector.
A Bragg crystal polarimeter for the focal plane of the SODART telescope on the Spectrum-X-Gamma mission is being designed. A mosaic graphite crystal will be oriented at 45 deg to the optic axis of the telescope, thereby preferentially reflecting those X-rays which satisfy the Bragg condition and have electric vectors that are perpendicular to the plane defined by the incident and reflected photons. The reflected X-rays will be detected by an imaging proportional counter with the image providing direct X-ray aspect information. The crystal will be about 50 microns thick to allow X-rays with energies of 4 keV or greater to be transmitted to a lithium block mounted below the graphite. The lithium is used to measure the polarization of these high energy X-rays by exploiting the polarization dependence of Thomson scattering. The development of thin mosaic graphite crystals is discussed and recent reflectivity, transmission, and uniformity measurements are presented.
Mechanisms of solar gamma radiation production - prediction of fluxes at earth
Results of new measurements of the total cosmic gamma-ray spectrum in the 0.3- to 27-MeV range obtained on Apollo 15. These data were obtained with an isotropic scintillation counter similar to that used on Ranger 3 and ERS-18. The new high-precision data permit extension and clarification of the spectrum above 1 MeV, where recent balloon and earth-satellite observations have caused doubts as to the validity of the ERS-18 data.
The Stellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources.
The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Currently, four of the modules are being fabricated by the Marshall Space Flight Center (MSFC.) Each MSFC module consist of 28 nested Ni/Co thin shells giving an effective area of 65 sq cm at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of these modules to the IKI is scheduled for summer 2013. We present a status of the ART x-ray modules development at the MSFC.
The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the ART-XC instrument on board the Spectrum-Roentgen Gamma Mission. Four of those modules are being fabricated under a Reimbursable Agreement between NASA and the Russian Space Research Institute (IKI.) An additional three flight modules and one spare for the ART-XC Instrument are produced under a Cooperative Agreement between NASA and IKI. The instrument will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Each module consists of 28 nested thin Ni/Co shells giving an effective area of 65 cm2 at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. Delivery of the first four modules is scheduled for November 2013, while the remaining three modules will be delivered to IKI in January 2014. We present a status of the ART x-ray module development at MSFC.
An analysis was made of data collected by Apollo 15 on the total cosmic gamma ray background over the 0.3 to 27 MeV range. Sources of interference with respect to the determination of diffused gamma ray spectrum were considered. Attempts were made to correct the measured spectrum for these background effects.
The Marshall Space Flight Center (MSFC) is developing x-ray mirror modules for the Astronomical Roengen Telescope- X-ray Concentrator (ART-XC) instrument on board the Spectrum-Roentgen-Gamma Mission. ART-XC will consist of seven co-aligned x-ray mirror modules with seven corresponding CdTe focal plane detectors. Each module provides an effective area of 65 sq cm at 8 keV, response out to 30 keV, and an angular resolution of 45 arcsec or better HPD. We will present a status of the ART x-ray module development at MSFC.
Balloon observation of upper limits of solar gamma rays for spectral ranges 20-200 kev and 1-10 mev
Cosmic gamma ray spectra from production and decay of neutral pi-mesons produced in metagalactic cosmic-ray proton-proton collisions
The Stellar X-Ray Polarimeter (SXRP) uses the polarization sensitivity of a graphite Bragg crystal and a lithium Thomsom scattering target to measure the polarization of X-rays from astrophysical sources. The SXRP is a focal plane detector for the Soviet-Danish SODART telescopes which will be launched on the Soviet Spectrum-X-Gamma mission. The SXRP will be the third orbiting stellar X-ray polarimeter, and should provide an order of magnitude increase in polarization sensitivity over its predecessors.
X-ray scattering from a lithium disk and Bragg reflection from a mosaic graphite crystal can be exploited to measure the linear polarization of radiation emitted from cosmic X-ray sources. The sensitivity is enhanced if the polarimeters are placed at the focus of an X-ray telescope. Such devices form two of the components of the Stellar X-ray Polarimeter experiment scheduled to fly on the Spectrum-X-Gamma mission. The expected on-axis performance of the two components is described based on detailed Monte Carlo simulations. The polarimetry experiment is expected to provide sensitive measurements of linear polarization for many cosmic X-ray sources. The nature and utility of such observations is described for pulsing X-ray sources such as the Crab pulsar and Her X-1.
X-ray scattering from a lithium disk and Bragg reflection from a mosaic graphite crystal can be exploited to measure the linear polarization of radiation emitted from cosmic X-ray sources. The sensitivity is greatly enhanced if these polarimeters are placed at the focus of an X-ray telescope. Such devices form two of the three components of the Stellar X-Ray Polarimeter experiment scheduled to fly on the Spectrum-X-Gamma mission. The experiment will reside at the focus of one of the SODART X-ray telescopes. The expected on-axis performance of these two components of the Stellar X-Ray Polarimeter experiment based on detailed Monte-Carlo simulation is described. Various systematic effects, both external and internal to the experiment, that must be considered in order to properly design and utilize the experiment are also discussed.
Cosmic gamma ray spectra near one MEV observed by ERS-18 satellite
Omnidirectional cosmic gamma ray flux near one MeV observed by ERS-18 satellite, plotting spectral energy distribution
A table of spectral features, including narrow, very broad, and 'photospheric' lines, in the ultraviolet spectrum of the Wolf-Rayet binary gamma(2) Velorum is given together with radial velocities at phase 0.99. The very broad lines display P Cygni profiles. Ten weak absorption features are tentatively assigned to blends of numerous lines of Fe IV, and three other similar features are possibly due to Fe V blends. These iron lines appear to be associated with the Wolf-Rayet component. The narrow features are present with a wide range of ionization. The Si IV, and probably C IV, features are circumstellar, while the other narrow absorptions are either interstellar or possibly a combination of interstellar and circumstellar. A model is proposed for the outer layers of the extended envelope of the Wolf-Rayet star.
The HEAO-3 High Resolution Gamma-Ray Spectrometer observed the Galactic center region in fall 1979 and in the spring of 1980. Variation of the positron annihilation line at 511 keV has been reported previously. The fall 1979 observations show a significant high-energy continuum at energies above 511 keV. The intensity of a possible positronium triplet-state continuum is found to be less than that expected for direct positron annihilation and positronium decay in an ionized, warm (T approximately equal to or less than 10 to the 5th K) plasma. Depending on assumption for the shape of the high-energy continuum spectrum, positronium fractions between 0.0 and 0.75 (at 90 percent statistical confidence level) are consistent with the observations.