The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform
R Ramaty - One of the best experts on this subject based on the ideXlab platform.
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nuclear deexcitation gamma ray Lines from accelerated particle interactions
Astrophysical Journal Supplement Series, 2002Co-Authors: B Kozlovsky, R J Murphy, R RamatyAbstract:Total cross sections for the production of Gamma-Ray Lines from nuclear deexcitation as a function of the projectile energy are evaluated and presented. Included are proton and α reactions with He, C, N, O, Ne, Mg, Al, Si, S, Ca, and Fe. Such functions are essential for interpretation of Gamma-Ray line observations of astrophysical sites which contain large fluxes of energetic particles such as solar flares, the Earth's atmosphere, planetary atmospheres and surfaces, the interstellar medium, and galactic nebulae.
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transient gamma ray spectrometer measurements of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
arXiv: Astrophysics, 2000Co-Authors: M J Harris, R Ramaty, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, H SeifertAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the WIND spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where Gamma-Ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines which are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where beta-decays on a time-scale of a few hours in an expanding envelope produce positrons that annihilate to generate a line which is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January - 1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
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transient gamma ray spectrometer observations of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
The Astrophysical Journal, 1999Co-Authors: M J Harris, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, R RamatyAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the Wind spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where γ-ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines that are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where β decays on a timescale of a few hours in an expanding envelope produce positrons that annihilate to generate a line that is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January-1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
G J Hurford - One of the best experts on this subject based on the ideXlab platform.
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first flight of the gamma ray imager polarimeter for solar flares grips instrument
arXiv: Instrumentation and Methods for Astrophysics, 2016Co-Authors: G J Hurford, Nicole Duncan, P Sainthilaire, Albert Y Shih, H M Bain, M Amman, Brent Mochizuki, J Hoberman, J OlsonAbstract:The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) is a balloon-borne telescope designed to study solar-flare particle acceleration and transport. We describe GRIPS's first Antarctic long-duration flight in Jan 2016 and report preliminary calibration and science results. Electron and ion dynamics, particle abundances and the ambient plasma conditions in solar flares can be understood by examining hard X-ray (HXR) and Gamma-Ray emission (20 keV to 10 MeV) with enhanced imaging, spectroscopy and polarimetry. GRIPS is specifically designed to answer questions including: What causes the spatial separation between energetic electrons producing HXRs and energetic ions producing Gamma-Ray Lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? GRIPS's key technological improvements over the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid, multi-pitch rotating modulator (MPRM) collimator. The 3D-GeDs have spectral FWHM resolution of a few hundred keV and spatial resolution $<$1 mm$^3$. For photons that Compton scatter, usually $\gtrsim$150 keV, the energy deposition sites can be tracked, providing polarization measurements as well as enhanced background reduction. The MPRM single-grid design provides twice the throughput of a bi-grid imaging system like RHESSI. The grid is composed of 2.5 cm thick W/Cu slats with 1-13 mm variable slit pitch, achieving quasi-continuous FWHM angular coverage over 12.5-162 arcsecs. This resolution is capable of imaging the separate magnetic loop footpoint emissions in a variety of flare sizes. (Abstract edited down from source.)
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first flight of the gamma ray imager polarimeter for solar flares grips instrument
Proceedings of SPIE, 2016Co-Authors: G J Hurford, Nicole Duncan, P Sainthilaire, Albert Y Shih, H M Bain, M Amman, Brent Mochizuki, J Hoberman, J OlsonAbstract:The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument is a balloon-borne telescope designed to study solar- are particle acceleration and transport. We describe GRIPS's first Antarctic long-duration flight in January 2016 and report preliminary calibration and science results. Electron and ion dynamics, particle abundances and the ambient plasma conditions in solar flares can be understood by examining hard X-ray (HXR) and Gamma-Ray emission (20 keV to 10 MeV). Enhanced imaging, spectroscopy and polarimetry of are emissions in this energy range are needed to study particle acceleration and transport questions. The GRIPS instrument is specifically designed to answer questions including: What causes the spatial separation between energetic electrons producing hard X-rays and energetic ions producing Gamma-Ray Lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? GRIPS's key technological improvements over the current solar state of the art at HXR/Gamma-Ray energies, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid modulation collimator, the multi-pitch rotating modulator (MPRM). The 3D-GeDs have spectral FWHM resolution of a few hundred keV and spatial resolution 3 . For photons that Compton scatter, usually g150 keV, the energy deposition sites can be tracked, providing polarization measurements as well as enhanced background reduction through Compton imaging. Each of GRIPS's detectors has 298 electrode strips read out with ASIC/FPGA electronics. In GRIPS's energy range, indirect imaging methods provide higher resolution than focusing optics or Compton imaging techniques. The MPRM gridimaging system has a single-grid design which provides twice the throughput of a bi-grid imaging system like RHESSI. The grid is composed of 2.5 cm deep tungsten-copper slats, and quasi-continuous FWHM angular coverage from 12.5-162 arcsecs are achieved by varying the slit pitch between 1-13 mm. This angular resolution is capable of imaging the separate magnetic loop footpoint emissions in a variety of are sizes. In comparison, RHESSI's 35-arcsec resolution at similar energies makes the footpoints resolvable in only the largest ares.
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first gamma ray images of a solar flare
The Astrophysical Journal, 2003Co-Authors: G J Hurford, S Krucker, R A Schwartz, D M Smith, N VilmerAbstract:Imaging of Gamma-Ray Lines, produced by nuclear collisions of energetic ions with the solar atmosphere, provides the only direct indication of the spatial properties of accelerated ions near the Sun. We present the first Gamma-Ray images of a solar flare, obtained with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for the X4.8 flare of 2002 July 23. Two rotating modulation collimators (with 35'' and 183'' resolution) were used to obtain images for the same time interval in four energy bands: the narrow deuterium line at 2.223 MeV formed by the thermalization and capture of neutrons produced in the collisions; the 3.25-6.5 MeV band that includes the prompt de-excitation Lines of C and O; and the 0.3-0.5 and 0.7-1.4 MeV bands that are dominated by electron bremsstrahlung. The centroid of the 2.223 MeV image was found to be displaced by 20'' ± 6'' from that of the 0.3-0.5 MeV image, implying a difference in acceleration and/or propagation between the accelerated electron and ion populations near the Sun.
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the reuven ramaty high energy solar spectroscopic imager rhessi
Solar Physics, 2003Co-Authors: R P Lin, G J Hurford, D M Smith, B R Dennis, A Zehnder, P R Harvey, D W Curtis, D Pankow, P Turin, M BesterAbstract:RHESSI is the sixth in the NASA line of Small Explorer (SMEX) missions and the first managed in the Principal Investigator mode, where the PI is responsible for all aspects of the mission except the launch vehicle. RHESSI is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/Gamma-Ray continua emitted by energetic electrons, and of Gamma-Ray Lines produced by energetic ions. The single instrument consists of an imager, made up of nine bi-grid rotating modulation collimators (RMCs), in front of a spectrometer with nine cryogenically-cooled germanium detectors (GeDs), one behind each RMC. It provides the first high-resolution hard X-ray imaging spectroscopy, the first high-resolution Gamma-Ray line spectroscopy, and the first imaging above 100 keV including the first imaging of Gamma-Ray Lines. The spatial resolution is as fine as ~ 2.3 arc sec with a full-Sun (≳ 1°) field of view, and the spectral resolution is ~ 1–10 keV FWHM over the energy range from soft X-rays (3 keV) to Gamma-Rays (17 MeV). An automated shutter system allows a wide dynamic range (> 107) of flare intensities to be handled without instrument saturation. Data for every photon is stored in a solid-state memory and telemetered to the ground, thus allowing for versatile data analysis keyed to specific science objectives. The spin-stabilized (~ 15 rpm) spacecraft is Sun-pointing to within ~ 0.2° and operates autonomously. RHESSI was launched on 5 February 2002, into a nearly circular, 38° inclination, 600-km altitude orbit and began observations a week later. The mission is operated from Berkeley using a dedicated 11-m antenna for telemetry reception and command uplinks. All data and analysis software are made freely and immediately available to the scientific community.
M J Harris - One of the best experts on this subject based on the ideXlab platform.
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transient gamma ray spectrometer measurements of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
arXiv: Astrophysics, 2000Co-Authors: M J Harris, R Ramaty, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, H SeifertAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the WIND spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where Gamma-Ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines which are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where beta-decays on a time-scale of a few hours in an expanding envelope produce positrons that annihilate to generate a line which is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January - 1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
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transient gamma ray spectrometer observations of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
The Astrophysical Journal, 1999Co-Authors: M J Harris, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, R RamatyAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the Wind spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where γ-ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines that are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where β decays on a timescale of a few hours in an expanding envelope produce positrons that annihilate to generate a line that is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January-1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
D M Smith - One of the best experts on this subject based on the ideXlab platform.
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first gamma ray images of a solar flare
The Astrophysical Journal, 2003Co-Authors: G J Hurford, S Krucker, R A Schwartz, D M Smith, N VilmerAbstract:Imaging of Gamma-Ray Lines, produced by nuclear collisions of energetic ions with the solar atmosphere, provides the only direct indication of the spatial properties of accelerated ions near the Sun. We present the first Gamma-Ray images of a solar flare, obtained with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for the X4.8 flare of 2002 July 23. Two rotating modulation collimators (with 35'' and 183'' resolution) were used to obtain images for the same time interval in four energy bands: the narrow deuterium line at 2.223 MeV formed by the thermalization and capture of neutrons produced in the collisions; the 3.25-6.5 MeV band that includes the prompt de-excitation Lines of C and O; and the 0.3-0.5 and 0.7-1.4 MeV bands that are dominated by electron bremsstrahlung. The centroid of the 2.223 MeV image was found to be displaced by 20'' ± 6'' from that of the 0.3-0.5 MeV image, implying a difference in acceleration and/or propagation between the accelerated electron and ion populations near the Sun.
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the reuven ramaty high energy solar spectroscopic imager rhessi
Solar Physics, 2003Co-Authors: R P Lin, G J Hurford, D M Smith, B R Dennis, A Zehnder, P R Harvey, D W Curtis, D Pankow, P Turin, M BesterAbstract:RHESSI is the sixth in the NASA line of Small Explorer (SMEX) missions and the first managed in the Principal Investigator mode, where the PI is responsible for all aspects of the mission except the launch vehicle. RHESSI is designed to investigate particle acceleration and energy release in solar flares, through imaging and spectroscopy of hard X-ray/Gamma-Ray continua emitted by energetic electrons, and of Gamma-Ray Lines produced by energetic ions. The single instrument consists of an imager, made up of nine bi-grid rotating modulation collimators (RMCs), in front of a spectrometer with nine cryogenically-cooled germanium detectors (GeDs), one behind each RMC. It provides the first high-resolution hard X-ray imaging spectroscopy, the first high-resolution Gamma-Ray line spectroscopy, and the first imaging above 100 keV including the first imaging of Gamma-Ray Lines. The spatial resolution is as fine as ~ 2.3 arc sec with a full-Sun (≳ 1°) field of view, and the spectral resolution is ~ 1–10 keV FWHM over the energy range from soft X-rays (3 keV) to Gamma-Rays (17 MeV). An automated shutter system allows a wide dynamic range (> 107) of flare intensities to be handled without instrument saturation. Data for every photon is stored in a solid-state memory and telemetered to the ground, thus allowing for versatile data analysis keyed to specific science objectives. The spin-stabilized (~ 15 rpm) spacecraft is Sun-pointing to within ~ 0.2° and operates autonomously. RHESSI was launched on 5 February 2002, into a nearly circular, 38° inclination, 600-km altitude orbit and began observations a week later. The mission is operated from Berkeley using a dedicated 11-m antenna for telemetry reception and command uplinks. All data and analysis software are made freely and immediately available to the scientific community.
D M Palmer - One of the best experts on this subject based on the ideXlab platform.
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transient gamma ray spectrometer measurements of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
arXiv: Astrophysics, 2000Co-Authors: M J Harris, R Ramaty, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, H SeifertAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the WIND spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where Gamma-Ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines which are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where beta-decays on a time-scale of a few hours in an expanding envelope produce positrons that annihilate to generate a line which is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January - 1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
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transient gamma ray spectrometer observations of gamma ray Lines from novae i limits on the positron annihilation line in five individual novae
The Astrophysical Journal, 1999Co-Authors: M J Harris, J E Naya, B J Teegarden, T Cline, N Gehrels, D M Palmer, R RamatyAbstract:The Transient Gamma Ray Spectrometer (TGRS) on board the Wind spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where γ-ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak Lines that are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where β decays on a timescale of a few hours in an expanding envelope produce positrons that annihilate to generate a line that is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January-1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.
