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NASA NTRS1991

X-ray echoes from gamma-ray bursts

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed.

Dermer, Charles D.↗

NASA NTRS1994

Gamma Ray Spectrometers

Gamma rays are high energy electromagnetic radiation with energies typically starting from a few tens of keV and extending to beyond TeV energies. Although gamma rays, like other electromagnectic radiation, can be characterized by frequency and wavelength, they are more particle-like in nature and carry energy, and momentum.

frequencywavelength↗

NASA NTRS1976

The relationship between the galactic matter distribution, cosmic ray dynamics, and gamma ray production

Theoretical considerations and analysis of the results of gamma ray astronomy suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density should be enhanced where the matter density is greatest on the scale of galactic arms. This concept has been explored in a galactic model using recent 21 cm radio observations of the neutral hydrogen and 2.6 mm observations of carbon monoxide, which is considered to be a tracer of molecular hydrogen. The model assumes: (1) cosmic rays are galactic and not universal; (2) on the scale of galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3) the cosmic ray scale height is significantly larger than the scale height of the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of about 3:1.

Kniffen, D. A.↗

NASA NTRS1971

Cosmic gamma rays

Cosmic gamma ray production processes, galactic and extragalactic gamma rays, and cosmology

Stecker, F. W.↗

NASA NTRS1985

The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy

High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer (GRIS) is one of the experiments selected as part of this program. The instrument contains a number of new and innovative features that are expected to produce a significant improvement in source location accuracy and sensitivity over previous balloon and satellite experiments.

Teegarden, B. J.↗

NASA NTRS1995

Observations and theory of X-rays and gamma-rays from radio-quiet Seyferts

Recent oriented scintillation spectrometer experiment (OSSE) observations of sift gamma-ray emission from radio-quiet Seyfert galaxies as well as their theoretical implications are reviewed. For some Seyferts, the OSSE data can be combined with X-ray data from Ginga and ROSAT. Seyfert 1s have intrinsic power-law spectra with approximately 0.9 extending without a break to at least approximately 200 keV. There is some evidence for a break at higher energies. On top of this intrinsic spectrum there is a Compton reflection component, which corresponds to cold matter covering a approximately 2 pi solid angle as seen by the power-law source. Compton reflection is responsible for a hardening of the spectrum in the approximately 5-30 keV range and a softening at approximately 30-200 keV. This spectrum is then abasorbed by a partially ionized external medium. The spectra of Seyfert 2s are marginally consistent with those of Seyfert 1s modified by strong absorption. However, there are indications that their intrinsic X-ray spectra are harder than those of Seyfert 1s. This is in fact the case for NGC 4151, a Seyfert 1.5. The Seyfert spectra integrated over redshift with cosmological evolution can explain the cosmic X-ray background spectrum from 1 to 100 keV.

Zdziuarski, A. A.↗

NASA NTRS1982

16 November 1979 gamma-ray bursts observed with HEAO-3 High-Resolution Gamma-Ray Spectrometer

On 1979 November 16, two gamma-ray bursts were observed by the High-Resolution Gamma-Ray Spectrometer on HEAO-3. The first event occurred at 14:16:41 U.T. and lasted about eight seconds. This event was detected only by the instrument's five CsI anticoincidence shield pieces. The second event occurred 61 sec later, at 14:17:42, and lasted about 18 sec. This event was clearly detected by the high-resolution germanium detectors. Because of the close temporal coincidence of the two events, the possibility is considered that both events originated from one celestial source, and that the scanning motion of HEAO-3 (nominal spin period 20 min) excluded the first from the approximately 30 deg FWHM field of view of the germanium detectors but included the second. Directional information from the relative response of the five shield pieces and the earth occultation constraint are all consistent with this interpretation and suggest a source location near RA equals 10 hr, Dec equals 45 deg. No significant spectral features appear in the high-resolution data from the second burst.

Wheaton, W. A.↗

NASA NTRS1974

Midlatitude electron precipitation: A possible source of contamination of galactic X and gamma-ray measurements

The effect of trapped and precipitated particles in the magnetosphere on the measurement of galactic X-rays and gamma rays is discussed. To minimize contamination caused by electron precipitation, most galactic X-ray and gamma ray measurements are conducted at equatorial or relatively low to middle latitudes where the influence of auroral effects is expected to be small. Substorm-related VLF phase perturbations also affect the measurements. If such perturbation are indicative of electron precipitation at middle to low latitudes, then their relatively high frequency of occurrence, as many as 100 per year, is evidence that electron precipitation at these latitudes may pose a problem to some galactic X-ray and gamma ray measurements. Charts and maps are presented to show: (1) phase recordings from sixteen sub-ionospheric VLF propagation paths, (2) map of great circle propagation paths, (3) ionization rates in the nighttime ionosphere due to several sources, and (4) computer phase variation for the NLK-APL path versus electron flux for different e-folding energies.

Rosenberg, T. J.↗

NASA NTRS2004

Swift Gamma-Ray Burst Explorer: Mission Design for Rapid, Accurate Location of Gamma-ray Bursts

The Swift Gamma-ray Burst Explorer is a NASA Mid-sized Explorer (MIDEX) with the primary mission of determining the origins of Gamma-Ray Bursts (GRBs). It will be the first mission to autonomously respond to newly-discovered GRBs and provide immediate follow-up narrow field instruments capable of multi-wavelength (UV, Optical, X-ray) observations. The characteristics of GRBs that are the key mission design drivers, are their non-repeating and brief duration bursts of multi-wavelength photons. In addition, rapid notification of the location and characteristics of the GRBs to ground-and-space- based observatories drive the end-to-end data analysis and distribution requirements. The Swift mission is managed by the GSFC, and includes an international team of contributors that each bring their unique perspective that have proven invaluable to the mission. The spacecraft bus, provided by Spectrum Astro, Inc. was procured through a Rapid Spacecraft Development Office (RSDO) contract by the GSFC. There are three instruments: the Burst Alert Telescope (BAT) provided by the GSFC; the X-Ray Telescope (XRT) provided by a team led by the Pennsylvania State University (PSU); and the Ultra-Violet Optical Telescope (UVOT), again managed by PSU. The Mission Operations Center (MOC) was developed by and is located at PSU. Science archiving and data analysis centers are located at the GSFC, in the UK and in Italy.

Bundas, David J.↗

NASA NTRS2004

Swift Gamma-Ray Burst Explorer: Mission Design for Rapid, Accurate Location of Gamma-ray Bursts

Bundas, David J.↗

NASA NTRS2005

Swift Gamma-ray Burst Explorer: Mission Design for Rapid, Accurate Location of Gamma-ray Bursts

Bundas, David J.↗

NASA NTRS1974

A new model of atmospheric gamma rays and its implications for measurement of diffuse cosmic gamma rays from within the atmosphere

A semi-empirical model is discussed which describes atmospheric gamma rays in the range 0.3 less then or equal to E less than or equal to 10 MeV based on the production per unit mass of air. The model is based on the concept of a source strength (photon/g sec MeV) which is energy- and depth-dependent, and derived from measured fluxes. Quantities such as directional fluxes, angular distributions, and growth curves are calculated directly from this model. The source function is described by four energy-dependent parameters determined empirically from fluxes measured with a 7.5 cm x 7.5 cm Nal counter over the atmospheric depth range from 3.5 to 500 g/sq cm. From S(E,x), obtained for both continuum and discrete gamma rays at lambda = 40 deg, the depth and angle dependence of directional fluxes were calculated. Growth-curve predictions needed to separate atmospheric from diffuse cosmic fluxes were determined.

Matteson, J. L.↗

NASA NTRS1990

Hard X-ray and gamma-ray imaging spectroscopy for the next solar maximum

The objectives and principles are described of a single spectroscopic imaging package that can provide effective imaging in the hard X- and gamma-ray ranges. Called the High-Energy Solar Physics (HESP) mission instrument for solar investigation, the device is based on rotating modulation collimators with germanium semiconductor spectrometers. The instrument is planned to incorporate thick modulation plates, and the range of coverage is discussed. The optics permit the coverage of high-contrast hard X-ray images from small- and medium-sized flares with large signal-to-noise ratios. The detectors allow angular resolution of less than 1 arcsec, time resolution of less than 1 arcsec, and spectral resolution of about 1 keV. The HESP package is considered an effective and important instrument for investigating the high-energy solar events of the near-term future efficiently.

Hudson, H. S.↗

NASA NTRS1977

Lunar surface chemistry of regions common to the orbital X-ray and gamma-ray experiments

Concentration ratios of Al/Si and Mg/Si have been determined from the orbital X-ray data for twenty-two regions for which the concentrations of Th, K, Fe, and Mg has previously been specified from orbital gamma-ray data. The strong anticorrelation between Fe and Al seen in returned samples is confirmed for large areas of the lunar surface. The natural radioactivity of the large maria increases from east to west whereas an inverse in true for the aluminum concentration. The difficulty in determining Mg concentrations in each experiment is discussed.

Bielefeld, M. J.↗

NASA NTRS1978

Large scale telescopes for high resolution X-ray and gamma-ray astronomy

This paper shows that angular-resolution, energy-range, and structural constraints on image-modulated X-ray telescopes are not fundamental and that the limits on angular resolution can be overcome by constructing such telescopes on a very large spatial scale. It is proposed that widely separated satellites be used for the modulating mask and detector array. Implementation of this concept is discussed in terms of a simple system consisting of a pinhole camera (i.e., a hole in an opaque mask on one subsatellite and a detector array on another). Advantages and problems of such systems are briefly discussed, and a solar X-ray telescope intended for deployment from a Shuttle orbiter is described. It is noted that such large-scale telescopes can be constructed to image gamma rays and even energetic neutrons as well.

Hudson, H. S.↗

NASA NTRS1995

Statistical properties of the time histories of cosmic gamma-ray bursts detected by the BATSE experiment of the Compton gamma-ray observatory

The main scientific objectives of the project were: (1) Calculation of average time history for different subsets of BATSE gamma-ray bursts; (2) Comparison of averaged parameters and averaged time history for different Burst And Transient Source Experiments (BASTE) Gamma Ray Bursts (GRB's) sets; (3) Comparison of results obtained with BATSE data with those obtained with APEX experiment at PHOBOS mission; and (4) Use the results of (1)-(3) to compare current models of gamma-ray bursts sources.

Sagdeev, Roald↗

NASA NTRS1978

Possible X-ray counterparts of gamma-ray sources

The results are presented of a survey regarding the X-ray source positions which fall within the error boxes of 10 unidentified gamma-ray sources observed with the aid of the COS-B satellite. In three cases, including CG 135-1, CG 312-1, and CG 327-0, an X-ray source was found within the gamma-ray error box. However, because of the large uncertainty regarding the gamma-ray source positions, the positional coincidence is not necessarily conclusive. It is, therefore, necessary to take into account additional information on the spectral or temporal characteristics of the X-ray sources. It is found that the X-ray source 4U 02416 plus 1 is a possible candidate as the X-ray-counterpart of CG 135 plus 1 in connection with both spectral hardness characteristics and positional coincidence.

Maraschi, L.↗

NASA NTRS1979

X-ray emission from gamma-ray sources in the galactic anticentre region

An X-ray survey of three high energy gamma-ray sources in the galactic anticenter region conducted using the large area sky survey instrument on HEAO 1 is presented. The sensitivity of this survey is highest reported, and two, and possibly three, X-ray sources were detected in the vicinity of gamma 195+5. Three new X-ray sources have been discovered within a few degrees of CG176-7, but none overlaps the gamma-ray error box. These results demonstrate that gamma-ray sources like CG195+4 and CG176-7 have emission characteristics different from the Crab pulsar, but may be similar to the Vela pulsar. Alternatively, the lack of detectable X-ray flux suggests that the gamma-ray emission arises from cosmic-ray interactions in dense interstellar clouds. An interesting feature of the new X-ray sources is that four of them may be associated with early-type stars which exhibit emission lines.

Share, G. H.↗