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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Gamma ray cosmology: The extra galactic gamma spectrum and methods to detect the underlying source

The possible sources of extragalactic gamma rays and methods to distinguish the different sources are discussed. The sources considered are early universe decays and annihilation of Particles, active galactic nuclei (AGN) sources, and baryon-antibaryon annihilation in a baryon symmetric cosmology. The energy spectrum and possible angular fluctuations due to these sources are described.

Cline, David B.↗
NASA NTRS1993

A Team Approach to the Development of Gamma Ray and x Ray Remote Sensing and in Situ Spectroscopy for Planetary Exploration Missions

An important part of the investigation of planetary origin and evolution is the determination of the surface composition of planets, comets, and asteroids. Measurements of discrete line X-ray and gamma ray emissions from condensed bodies in space can be used to obtain both qualitative and quantitative elemental composition information. The Planetary Instrumentation Definition and Development Program (PIDDP) X-Ray/Gamma Ray Team has been established to develop remote sensing and in situ technologies for future planetary exploration missions.

Trombka, J. I.↗
NASA NTRS1974

A burst of energetic gamma rays

A burst of gamma rays with energies greater than 1 MeV occurring on May 14, 1972, at 201247 UT (151247 local time) was detected during a balloon flight from Palestine, Texas, at a float altitude of 4g/sq cm residual atmosphere. The detector was a tank of liquid scintillator 1m x 0.5 m x 15 cm surrounded by a 0.6 cm plastic scintillator in anticoincidence. The signal was 60 standard deviations above a steady background of 600 counts/sec. The flux was 0.12 (+0.07 or -0.04) gamma/sq cm, and the time integrated flux 20(+11 or -7) gamma/sq cm. Only one such event was seen during the 8 hours of observation in the daytime on May 14 and 15. Two sub-flares in H alpha occurred during the burst, but not coincident with the start time. A detector on the Solrad satellite observed X-rays on all channels 2 minutes after the gamma ray start time. This event is similar to three earlier reported events.

Koga, R.↗
NASA NTRS1997

Charged Particle Induced Radiation damage of Germanium Detectors in Space: Two Mars Observer Gamma-Ray Detectors

The Mars Observer Gamma-Ray Spectrometer (MO GRS) was designed to measure gamma-rays emitted by the Martian surface. This gamma-ray emission is induced by energetic cosmic-ray particles penetrating the Martian surface and producing many secondary particles and gamma rays. The MO GRS consisted of an high-purity germanium (HPGe) detector with a passive cooler. Since radiation damage due to permanent bombardment of energetic cosmic ray particles (with energies up to several GeV) was expected for the MO GRS HPGe crystal, studies on radiation damage effects of HPGe crystals were carried on earth. One of the HPGe crystals (paradoxically called FLIGHT) was similar to the MO GRS crystal. Both detectors, MO GRS and FLIGHT, contained closed-end coaxial n-type HPGe crystals and had the same geometrical dimensions (5.6 x 5.6 cm). Many other parameters, such as HV and operation temperature, differed in space and on earth, which made it somewhat difficult to directly compare the performance of both detector systems. But among other detectors, detector FLIGHT provided many useful data to better understand radiation damage effects.

Bruekner, J.↗
NASA NTRS2008

Observing Gamma-ray Bursts with GLAST

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high-energy gamma-ray sky. The Large Area Telescope, the main instrument, is a pair-conversion telescope which will survey the sky in the energy range 20 MeV to greater than 300 GeV. The LAT's wide field of view (greater than 2 sr), large effective area and low deadtime combine to provide excellent high-energy gamma-ray observations of GRB. To tie these frontier high-energy observations to the better-known properties at lower energies, a second instrument, the GLAST Burst Monitor (GBM) will provide important spectra and timing in the 8 keV to 30 MeV range. Upon detection of a GRB by the LAT or the GBM, the spacecraft can autonomously repoint to keep the GRB location within the LAT field of view, allowing high-energy afterglow observations. We describe how the instruments, spacecraft, and ground system work together to provide observations of gamma-ray bursts from 8 keV to over 300 GeV and provide rapid notification of these observations to the wider gamma-ray burst community. Analysis and simulation tools dedicated to the GRB science have been developed. In this contribution we show the expected LAT sensitivity obtained with such simulations, and illustrate the results we expect from GLAST observations with spectral and temporal analysis of simulated GRB.

McEnery, Julie↗
NASA NTRS1993

Pulsed high-energy gamma rays from PSR 1055-52

The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory has detected a high-energy gamma-ray source at a position coincident with that of the radio pulsar PSR 1055-52. Analysis of the EGRET data at the radio pulsar period of 197 ms has revealed pulsed gamma-radiation at energies above 300 MeV, making PSR 1055-52 the fifth detected high-energy gamma-ray pulsar. The pulsed radiation from PSR 1055-52 has a very hard photon spectral index of -1.18 +/- 0.16 and a high efficiency for converting its rotational energy into gamma-rays. No unpulsed emission was observed.

Fierro, J. M.↗
NASA NTRSDate not supplied

AstroPix: ATLAS-Inspired Silicon Pixels for Future Space-Based Gamma-ray Telescopes

Space-based gamma-ray telescopes such as the Fermi Large Area Telescope have used single sided silicon strip detectors to measure the position of incident gamma-rays with high resolution. At lower energies, two dimensional position information within a single detector is required. This talk investigates the use of monolithic CMOS active pixel silicon sensors –AstroPix – as a novel technology for use in future gamma-ray telescopes. Based upon detectors designed for use in the ATLAS detector at the LHC, AstroPix has the potential to maintain the high energy and angular resolution required of a medium-energy gamma-ray telescope while reducing noise with the dual detection and readout capabilities of a CMOS chip. The status of AstroPix development and testing, as well as outlook for application in future telescopes such as the proposed medium-energy gamma-ray telescope AMEGO-X, will be presented.

Amanda L. Steinhebel↗
NASA NTRS1989

Simulating The Gamma-Ray Observatory Spacecraft

Gamma-Ray Observatory (GRO) spacecraft constitutes major advance in gamma-ray astronomy by offering first opportunity for comprehensive observations in range of 0.1 to 30,000 MeV. GRO Attitude Dynamics Simulator (GROSS) computer program designed to simulate mission. Consists of three separate programs: stand-alone profile program; simulator program, containing simulation control input/output (SCIO) subsystem, truth model (TM) subsystem, and on-board computer (OBC) subsystem; and postprocessor program. Written in FORTRAN 77.

Garrick, J.↗
NASA NTRS2011

The Fermi Gamma-Ray Space Telescope

This slide presentation reviews the Gamma Ray Astronomy as enhanced by the Fermi Gamma Ray Space Telescope and Radio Astronomy as a synergistic relationship. Gamma rays often represent a significant part of the energy budget of a source; therefore, gamma-ray studies can be critical to understanding physical processes in such sources. Radio observations offer timing and spatial resolutions vastly superior to anything possible with gamma-ray telescopes; therefore radio is often the key to understanding source structure. Gamma-ray and radio observations can complement each other, making a great team. It reviews the Fermi Guest Investigator (GI) program, and calls for more cooperative work that involves Fermi and the Very Long Baseline Array (VLBA), a system of ten radio telescopes.

Thompson, Dave↗
NASA NTRS1973

Ultra-high energy gamma rays

The production of ultrahigh energy gamma rays by proton interactions with relicit radiation, propagation of gamma rays through the universe, and proton cascading in the presence and absence of galactic magnetic fields is discussed. Detailed data are given on proton spectrum link, gamma ray intensity, and energy spectra of gamma rays on production.

Strong, A. W.↗
NASA NTRS2010

Exploring the Extreme Universe with the Fermi Gamma-Ray Space Telescope

Because high-energy gamma rays are produced by powerful sources, the Fermi Gamma-ray Space Telescope provides a window on extreme conditions in the Universe. Some key observations of the constantly changing gamma-ray sky include: (1) Gamma-rays from pulsars appear to come from a region well above the surface of the neutron star; (2) Multiwavelength studies of blazars show that simple models of jet emission are not always adequate to explain what is seen; (3) Gamma-ray bursts can constrain models of quantum gravity; (4) Cosmic-ray electrons at energies approaching 1 TeV suggest a local source for some of these particles.

Thompson, D. J.↗
NASA NTRS1991

The gamma-ray observatory

An overview is given of the Gamma Ray Observatory (GRO) mission. Detection of gamma rays and gamma ray sources, operations using the Space Shuttle, and instruments aboard the GRO, including the Burst and Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET) are among the topics surveyed.

Source record↗
NASA NTRS2007

Gamma-ray Astronomy and GLAST

The high energy gamma-ray (30 MeV to 100 GeV) sky has been relatively poorly studied. Most of our current knowledge comes from observations made by the Energetic Gamma Ray Experiment Telescope (EGRET) detector on the Compton Gamma Ray Observatory (CGRO), which revealed that the GeV gamma-ray sky is rich and vibrant. Studies of astrophysical objects at GeV energies are interesting for several reasons: The high energy gamma-rays are often produced by a different physical process than the better studied X-ray and optical emission, thus providing a unique information for understanding these sources. Production of such high-energy photons requires that charged particles are accelerated to equally high energies, or much greater. Thus gamma-ray astronomy is the study of extreme environments, with natural and fundamental connections to cosmic-ray and neutrino astrophysics. The launch of GLAST in 2008 will herald a watershed in our understanding of the high energy gamma-ray sky, providing dramatic improvements in sensitivity, angular resolution and energy range. GLAST will open a new avenue to study our Universe as well as to answer scientific questions EGRET observations have raised. In this talk, I will describe the GLAST instruments and capabilities and highlight some of the science we expect to address.

McEnery, Julie↗
NASA NTRS1992

Ulysses/BATSE observations of cosmic gamma ray bursts

The gamma ray burst detector aboard the ESA-NASA Ulysses spacecraft, in operation since Nov. 1990, has detected numerous gamma bursts in conjunction with the BATSE experiment aboard the Compton Observatory. Initial results are presented on burst locations for three events (21 April, 2 May, and 3 May, 1991) obtained by arrival time analysis, and they are compared with the BATSE locations. The arrival time analysis annuli have typical widths of 5'. The preliminary analysis indicates that both experiments are likely to have unresolved systematic errors, but that further work will improve the location accuracy substantially.

Hurley, K.↗
NASA NTRS1985

Gamma-Ray Observatory

The Gamma-Ray Observatory (GRO) will be placed in orbit by the Space Shuttle in the latter part of 1988. This large observatory weighs approximately 34,000 pounds, and the main body measures 25-feet long and 15-feet high and wide. The GRO will carry four scientific instruments that measure the gamma-ray spectrum from the end of the X-ray spectrum to the very high energy gamma. This paper primarily discusses the GRO's design and the procedures that relate to on-orbit servicing and maintenance. The original design of GRO was based on using some of the multimission modules from the Solar-Maximum Mission (SMM). The use of these modules and the increased use of astronauts in space activities has resulted in designs that, hopefully, will make GRO a more versatile observatory.

Madden, J. J.↗
DOE OSTI2021

Effects of Shielding on Gamma Rays [Slides]

The interaction of gamma rays with matter results in an effect we call attenuation (i.e. ‘shielding’). Attenuation can dramatically alter the appearance of a spectrum. Attenuating materials may actually create features in a spectrum via x-ray fluorescence. Attenuation is a function of the incident gamma-ray, material properties, and the thickness of the material. Half Value Layers (HVL) are a useful concept for estimating how much a given thickness of material will impact transmission of gamma-rays. Shielding impacts spectra in predictable ways. We can use clues in the spectrum to infer information about the source’s local environment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRSDate not supplied

Origin of High-Energy Protons Responsible for Late-Phase Pion-Decay Gamma-Ray Continuum from the Sun

Gamma-ray emission from solar eruptions can last far beyond the impulsive phase of the associated flares, and hence termed as sustained gamma-ray emission (SGRE). These gamma-rays result from the decay of neutral pions produced when >300 MeV protons collide with hydrogen and heavier elements in the solar photosphere. The source of protons producing SGRE has two possible origins: (i) particles accelerated in the associated flare are somehow trapped in magnetic structures and diffuse slowly to the chromosphere, and (ii) particles accelerated at the shock front that diffuse back to the Sun. In this presentation, we compile currently available observations and inferences that support these two possibilities. We use the gamma-ray data from the Fermi Large Area Telescope (Fermi/LAT) in conjunction with coronal mass ejection (CME) data from the Solar and Heliospheric Observatory (SOHO) and type II radio burst information from the Wind spacecraft. We also use the GOES soft X-ray flare information.

Nat Gopalswamy↗