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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Gamma-ray burster counterparts - Archival data

This paper reports on the results of a search for optical transient images associated with gamma-ray bursters based on the collection of archival photographs at the Harvard College Observatory. This study searched through over 32,000 plates showing 16 gamma-ray burst error regions. The primary result is the identification of three optical transient images. The recurrence time scale for optical events with a gamma-ray to optical fluence ratio of less than 1000 is estimated to be 1.3 yr (with a 99-percent confidence interval of between 0.41 and 4.8 yr). A control study was simultaneously made where regions of the sky with no bursters were examined. The control region was 15.6 times larger than the burst search region, yet no optical transients were found. This paper describes in detail the methodology and the statistical results. Close attention is paid to a detailed analysis of the three optical transient images.

Schaefer, Bradley E.↗
DOE OSTI2020

Modeling Aerial Gamma-Ray Backgrounds Using Non-negative Matrix Factorization

Airborne gamma-ray surveys are useful for many applications, ranging from geology and mining to public health and nuclear security. In all these contexts, the ability to decompose a measured spectrum into a linear combination of background source terms can provide useful insights into the data and lead to improvements in the techniques that use spectral energy windows. Multiple methods for the linear decomposition of spectra exist but are subject to various drawbacks, such as allowing negative photon fluxes or requiring detailed Monte Carlo modeling. In this work, we propose using non-negative matrix factorization (NMF) as a data-driven approach to spectral decomposition. Using aerial surveys that include flights over water, we demonstrate that the mathematical approach of NMF finds physically relevant structure in the aerial gamma-ray background, namely, that measured spectra can be expressed as the sum of nearby terrestrial emission, distant terrestrial emission, and radon and cosmic emission. Furthermore, these NMF background components are compared with the background components obtained by noise-adjusted singular value decomposition (NASVD), which contain negative photon fluxes and, thus, do not represent the emission spectra in as straightforward a way. Finally, we comment on the potential areas of research that are enabled by NMF decompositions, such as new approaches to spectral anomaly detection and data fusion.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1997

Analysis of Data from the Transient Gamma-Ray Spectrometer Experiment on the GGS/Wind Spacecraft

The data analysis from the TGRS experiment is continuing, although the UC Berkeley PI, K. Hurley, is no longer funded for this effort. This experiment has been returning data on the energy spectra and time histories of cosmic gamma-ray bursts since November 1994, and continues to operate in good health. Over a 3 year period ending in November 1997, 41 bursts have been detected simultaneously by TGRS and Dr. Hurley's Ulysses gamma-ray burst experiment. By comparing the times of arrival of a burst at Ulysses and TGRS, we can obtain an annulus of arrival directions for the event. Typical 3sigma annulus widths range from several arcminutes to tens of arcminutes. Because the WIND spacecraft is as far as several light-seconds from Earth, it is sometimes possible to obtain a second annulus using the Burst and Transient Source Experiment (BATSE) aboard the GRO spacecraft. 23 of the 41 bursts were also observed by this experiment. Generally, the two annuli intersect at grazing incidence, leading to a long, narrow error box which reduces somewhat the error circles obtained from BATSE alone. Table 1 summarizes the burst data from TGRS. We plan to defer the publication of these locations until a larger number of events has been accumulated. Measuring the energy spectra of cosmic gamma-ray bursts to search for line emission is one of the prime objectives of this experiment. However, an intense gamma-ray burst is required, or the statistics become too weak to draw meaningful conclusions. One such event has occurred to date, on August 22, 1995, and we have examined it in detail. The spectrum shows no evidence for lines, however.

Hurley, K.↗
NASA NTRS2017

Ionizing Organic Compound Based Nanocomposites for Efficient Gamma-Ray Sensor

Thin film and nanocrystalline materials of oxides have been very attractive choice as low cost option for gamma-ray detection and have shown great promise. Our studies on pure oxide films indicated that thickness and microstructure have pronounced effect on sensitivity. Since the interaction of gamma-ray with composites involves all three interaction processes; photoelectric effect, Compton scattering, and pair production, composites containing ionic organics have better chance for enhancing sensitivity. In the composites of ionizing organics oxidation effect of unusual oxides changes much faster and hence increases the sensitivity of radiation. In this study, we have used nickel oxide and titanium oxide in ionic organics to develop composite materials for low energy gamma-ray sensing. We prepared composites containing ethylene carbonate and evaluated the effect of commercial Cs-137 radiation source by studying current-voltage relationship at several frequencies. Radiated samples showed higher resistivity compared to as prepared composites.

Singh, N. B.↗
NASA NTRS1994

Gamma-ray properties of active galactic nuclei

Recent observations by the Compton Observatory (CGRO) have increased our knowledge about the gamma-ray emission from Active Galactic Nuclei (AGN) considerably. The three most important findings of CGRO with respect to AGNs are: first, no Seyfert 1 galaxy has been found to show emission above 500 keV. The by far strongest Seyfert 1 galaxy NGC 4151 shows a spectrum which falls off exponentially with an e-folding energy of 39 keV between 65 and 500 keV. OSSE so far has detected or has indications of detections for seven additional Seyfert 1 galaxies, which, however, all show very weak hard X-ray emission compared to NGC 4151. No annihilation feature has been seen from any Seyfert galaxy to this date. Second, the radio galaxy Cen A shows a power-law energy spectrum from hard X-ray energies of about 150 keV to at least 3 MeV. It has not been seen at EGRET-energies. Third, a new class of AGN was discovered at energies above 100 MeV by EGRET. The power of these objects in gamma-rays can dominate the luminosity in other spectral ranges. These objects are associated with extragalactic sources that have blazar properties. The high-energy gamma-ray emission is probably produced in relativistically outflowing jets. At hard X-ray energies the objects are rather weak. Spectral breaks at MeV energies were found by COMPTEL for three of these objects (3C 273, 3C 279, and PKS 0528+134).

Schoenfelder, V.↗
NASA NTRS1992

Gamma ray observations of the Crab pulsar - Past, present, future

The paper describes some of the high-energy observations of the Crab-Nebula pulsar, PSR0531+22. The pulse profiles of the Crab pulsar obtained in balloon-borne observations in 1967 and 1980 are presented. At present, gamma-ray scintillation detectors aboard the Gamma Ray Observatory (GRO) form the basis of the Burst and Transient Source Experiment (BATSE). The pulsar, which is observed daily by the BATSE, is used by all four GRO/BATSE detectors as a calibration source since it emits a steady, strong, well-known spectrum of gamma rays over the entire energy range to which detectors are sensitive. The paper presents an example of a pulse profile obtained with the BATSE.

Fishman, Gerald J.↗
NASA NTRS1980

The HEAO 3 gamma-ray spectrometer

The third High Energy Astronomy Observatory (HEAO 3), successfully launched into low earth orbit on September 20, 1979, carries a large high-resolution gamma-ray spectrometer designed for cosmic nuclear spectroscopy. This gamma-ray spectrometer (the HEAO C-1 experiment) consists of a cluster of four coaxial high-purity germanium detectors, each with a volume of approximately 100 cu cm. Surrounding the germanium detectors is a 6.6-cm thick CsI shield operating in active anticoincidence with the central detectors and defining a field of view of about 30 deg FWHM. An initial energy resolution of 3 keV FWHM at 1.46 MeV was achieved for each detector. All valid events in the germanium detectors are individually analyzed by an 8192-channel pulse area analyzer and transmitted at a maximum rate of 15.6 evens/s for each detector. During a 6-month mission, the experiment will perform a complete sky survey for narrow cosmic gamma-ray line emission to the sensitivity level of about 0.0001 photons/sq cm s over an operating energy range of 0.05-10 MeV.

Mahoney, W. A.↗
NASA NTRS1973

Cosmic soft gamma-ray bursts and the stellar super-flare hypothesis

Cosmic soft gamma ray bursts are discussed, and the stellar super-flare hypothesis is supported. Previous predictions and observations of gamma ray bursts are cited. Studies show that it is plausible that the bursts are caused by the bremsstrahlung of electrons accelerated to high energies in a stellar flare event. Possible observational consequences are listed for the stellar flare hypothesis.

Stecker, F. W.↗
NASA NTRS1991

Search for TeV gamma-ray emission from Hercules X-1

Six years of observations of Hercules X-1 with the Whipple Observatory gamma-ray telescope have been subjected to a Fourier analysis to search for emission at the 0.8079 Hz neutron star frequency. Evidence for a signal is found at the 99.5 percent confidence level for data taken with the medium-resolution imaging camera with some indications of emission at frequencies blueshifted from the fundamental frequency. However, analysis of the high-resolution camera data base have failed to substantiate this effect. Selection of events on the basis of gamma-ray-like image parameters did not enhance the signal from the medium-resolution data nor produce any indication of a signal from the high-resolution data. The overall conclusion is that no statistically significant evidence for TeV gamma-ray emission was found in the Whipple Observatory data base when the 6 years of data are taken as a whole.

Reynolds, P. T.↗
NASA NTRS2005

Gamma-Ray Spectral State Transitions of GRO J1719-24

We report the results of an in-depth study of the long-term soft gamma-ray (30 keV to 1.7 MeV) flux and spectral variability of the transient source GRO J1719-24 that was first discovered by BATSE and SIGMA in the fall of 1993. Our results were obtained from the JPL BATSE-EBOP database covering a 1000 day period between 1993 January 13 and 1995 October 10. During this period, the source underwent a major outburst in the fall of 1993 when the 35-100 keV flux rose from a quiescent state of less than 16 mcrab before 1993 September 17 to a level of 1.5 crab on October 3. The source remained in this high-intensity state over the next approx. 70 days, during which the 35-100 keV flux decreased monotonically by 33% to 1 crab on December 12, then decreased sharply to the pretransition quiescent level of 44 mcrab on December 21, where it remained until 1994 September 5. During a 400 day period between 1994 September 5 and 1995 October 10, the source again underwent a series of five transitions when the 35-100 keV flux increased to low-intensity levels of 200 400 mcrab, a factor of 4-7 times lower than what was observed in 1993. The low- and high-intensity states were characterized by two different spectral shapes. The low-state spectra are described by a power law with a spectral index of approx. 2. The high-state spectra, on the other hand, have two components: a thermal Comptonized shape below approx. 200 keV with electron temperature k(sub Te) of approx. 37 keV and optical depth tau approx. 2.8, and a soft power-law tail with photon index of 3.4 above 200 keV that extends to approx. 500 keV. The softer high-intensity spectrum and the harder low-intensity spectrum intersect at approx. 400 keV. The nonthermal power-law gamma-ray component in both the high- and low-intensity spectra suggests that the persistent nonthermal emission source is coupled to the hot and variable thermal emission source in the system. Furthermore, the correlation of the spectral characteristics with the high- and low-intensity states resembles that seen in two other gamma-ray emitting black hole candidates, GRO J0422+32 and Cygnus X-1, suggesting that perhaps similar system configurations and processes are occurring in these systems. Possible scenarios for interpreting these behaviors are discussed.

gamma rays↗
DOE OSTI2025

Neutron and Gamma-Ray Imaging of Th-232 and Cm-244 Using Organic Glass Scintillators

Modern nuclear safeguards require detection and characterization capabilities suitable for a wide variety of radiation sources and applications. Field-deployable detection systems have also had to modernize to meet changing needs. Recent developments in organic scintillator technology have resulted in the creation of an organic glass scintillator (OGS) at Sandia National Laboratory which is composed of a 9:1 mixture of glass compounds C42H36Si and C51H44Si. The novel scintillator composition was implemented into the design for a dual-particle capable imaging system at the University of Michigan. This work presents new results from two experiments demonstrating the gamma-ray and fast-neutron imaging capabilities of the organic glass system. Gamma spectroscopy was also performed using CeBr3 scintillators that are part of the imager design. Measurements were performed at Lawrence Livermore National Laboratory using 232Th metal hemishells and an encapsulated 244Cm oxide source. Successful gamma-ray imaging of the 232Th distributed sources is demonstrated with the glass imager, but there were no appreciable neutrons from the 232Th for neutron imaging. Promising neutron and gamma-ray imaging results of 244Cm are demonstrated despite limited imaging event statistics available in this measurement. Gamma-ray spectroscopy results were able to identify 232Th using prominent emissions at 239, 338, 583, and 911 keV. 244Cm was identified from emissions of 43, 99, and 153 keV. These results demonstrate the potential of organic glass imaging for nuclear nonproliferation or characterization efforts.

Lopez, Ricardo [Univ. of Michigan, Ann Arbor, MI (↗
DOE OSTI2020

GeMini: A High-Resolution, Low-Resource, Gamma-Ray Spectrometer for Planetary Science Applications

GeMini is a high-resolution gamma-ray spectrometer designed for planetary-science exploration. GeMini serves as the basis for instruments being flown on three upcoming deep-space missions: NASA’s mission to the M-class asteroid (16) Psyche, the Japan Aerospace Exploration Agency sample-return mission to the moons of Mars, and NASA’s Dragonfly mission that will land on Saturn’s largest moon, Titan. These science missions require high-resolution spectroscopy in a low-power, low-mass, rugged design that can survive in a variety of environments. GeMini addresses these needs by providing a cryogenically cooled crystal of high-purity germanium that can operate with as little as 10 to 20 watts, depending on the implementation and mission, and has a mass of less than 2 kg. GeMini helps determine the elemental composition of planetary bodies by measuring gamma rays emitted from the surface. This paper describes the mechanical, thermal, and electrical design of GeMini as well as its performance. Further, it describes testing that was performed to validate the design with respect to launch loads and radiation damage. Although the basic design of GeMini is common to all three missions, each planetary body has unique environmental conditions and mission specifications. This paper concludes by describing these upcoming missions and how GeMini is customized for each.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Optical studies of the regions of the gamma-ray bursts of 19 November, 1978 and 5 March, 1979

Optical studies were made of two well-located gamma-ray burst regions in the Southern Hemisphere using the 1.5 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Multi-filter image tube plates and UBV photometry surveys were made of both regions. The field of the 19 November, 1978 gamma-ray burst shows no early star or star with unusual colors out to several diameters of the nominal error box. The region of the 5 March, 1979 gamma-ray burst, which includes N49, contains several blue giants in the LMC, two of which deserve further study.

Fishman, G. J.↗
DOE OSTI2021

Branching ratios for the three most intense gamma rays in the decay of 47 Ca

A sample of 47 Ca produced through isotope harvesting at the National Superconducting Cyclotron Laboratory was used to measure branching ratios of 7.17(5)%, 7.11(5)%, and 75.0(5)% for the 489.2, 807.9, and 1297.1 keV characteristic gamma rays, respectively. Based on these updated branching ratios, the ground state to ground state 47 Ca to 47 Sc beta decay branching ratio has been indirectly measured as 17.7(5)% and the ground state to 1297.1 keV excited state as 82.2(5)%. Here these values represent a greatly increased precision for all five branching ratios compared to the currently accepted values. The measurements presented here were made relative to the ingrown 47Sc daughter in a 47 Ca sample and the well-established 159.4 keV gamma-ray branching ratio and the half-life for the decay of 47 Sc. These measurements were supported by verifying that the half-lives measured from characteristic gamma-ray peaks over multiple spectra for both 47 Ca and 47 Sc were consistent with previously reported values. Additionally, the half-lives of both 47 Ca and 47 Sc were independently measured with Liquid Scintillation Counting to reverify the previously reported values used in this study to find updated gamma-ray branching ratio values.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1984

The gamma-ray spectrum of Centaurus A - A high-resolution observation between 70 keV and 8 MeV

The NASA/Goddard Space Flight Center Low Energy Energy Gamma ray Spectrometer (LEGS) observed the nearby active nucleus galaxy Centaurus A (NGC 5128) during a balloon flight on 1981 November 19. There is no evidence of a break in the spectrum or of any line features. The 1.6 MeV limit is a factor of 8 lower than the 1974 line flux, indicating that, if the 1974 feature was real, and, if it was narrow, then the line intensity decreased significantly between 1974 and 1981. The lack of observed annihilation radiation from Cen A, combined with the temporal variations that are seen in the X-ray and gamma-ray intensities, constrain the size of the emission region to be between 10 to the 13th power and 5 x 10 to the 17th power cm. Previously announced in STAR as N83-35990

Gehrels, N.↗
NASA NTRS2005

How Special Are Dark Gamma-Ray Burst: A Diagnostic Tool

We present here a comprehensive study of the optical/near-infrared (IR) upper limits for gamma-ray bursts that have an X-ray afterglow. We have extrapolated the X-ray afterglows to optical wavelengths based on the physics of the fireball blast wave model and compared these results with optical upper limits for a large sample of bursts. We find a small set of only three bursts out of a sample of 20 for which the upper limits are not compatible with their X-ray afterglow properties within the context of any blast wave model. This sparse sample does not allow us to conclusively determine the cause of this optical/near-IR deficit. Extinction in the host galaxy is a likely cause, but high redshifts and different afterglow mechanisms might also explain the deficit in some cases. We note that the three bursts appear to have higher than average gamma-my peak fluxes. In a magnitude versus time diagram the bursts are separated from the majority of bursts with a detected optical/near-IR afterglow. However, two gamma- ray bursts with an optical afterglow (one of which is highly reddened) also fall in this region with dark bursts, making it likely that dark bursts are at the faint end of the set of optically detected bursts, and therefore the dark bursts likely form a continuum with the bursts with a detected optical afterglow. Our work provides a useful diagnostic tool for follow-up observations for potentially dark bursts; applied to the events detected with the Swift satellite, it will significantly increase our sample of truly dark bursts and shed light upon their nature. Subject headings: dust, extinction - gamma rays: bursts Online material: machine-readable tables

Rod, Evert↗
NASA NTRS1985

On the emission region of gamma ray bursts

Within the last few years the rapid accumulation of gamma ray burst spectral data, especially those of KONUS and solar maximum mission, has made the confrontation between theories of the gamma ray emission mechanisms and observations much more urgent and challenging. At present the most viable mode seems to be some combination of inverse Comptonization and synchrotron emission. Here, an attempt is made to limit the acceptable parameter space of the emission region by taking into account the maximum set of observational constraints. These are then applied to two specific scenarios: surface emission versus magnetospheric emission. Some observable predictions based on these scenarios are considered.

Liang, E. P.↗