The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
W R Purcell - One of the best experts on this subject based on the ideXlab platform.
-
The distribution of galactic 511 keV positron Annihilation Radiation
AIP Conference Proceedings, 2008Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:The Oriental Scintillation Spectrometer Experiment (OSSE) on NASA’s Compton Gamma‐Ray Observatory has completed numerous observations of the Galactic plane and Galactic center region. A principle objective of these observations was to measure the distribution of the Galactic positron Annihilation Radiation. Most of these observations provided positive detections of the narrow 511 keV Annihilation line. These data were fitted using several diffuse distribution models representing various populations of progenitor objects. The only model investigated which is not rejected is a two‐component distribution consisting of spheroidal and disk components; all other models investigated can be rejected at the ≳4.5σ confidence level. The size of the spheroidal component is found to be
-
positron Annihilation Radiation from the inner galaxy
The Astrophysical Journal, 2001Co-Authors: R L Kinzer, P A Milne, J D Kurfess, M S Strickman, W N Johnson, W R PurcellAbstract:The OSSE instrument on the Compton Gamma Ray Observatory (CGRO) was used to measure the one-dimensional latitudinal and longitudinal distributions of positron Annihilation Radiation (Annihilation line and positronium continuum components) along the inner Galactic ridge. Intensity measurements near the Galactic center (differential relative to background fields offset by 9°-12°) show a symmetrical and spatially narrow bulge around the center (effective FWHMs of 49 ± 07 in Galactic latitude and 63 ± 15 in longitude) with significant disk contributions to at least 35° in longitude. The latitude width of the Galactic plane emission away from the Galactic center is only weakly constrained in the current analysis. The longitudinal distribution is well fitted by either a model comprising a narrow (~63 FWHM ) Gaussian bulge plus ~35° FWHM Gaussian and CO-like disk components, or by a center-truncated R1/4 spheroid plus exponential disk model. For the latter model, the observed narrow latitudinal distribution near the Galactic center suggests that the bulge is ellipsoidal, although the fits are consistent with a spherical bulge as well. The positronium fraction estimate from the Galactic center direction is 0.93 ± 0.04. This, combined with the existing narrow line width measurements for the 511 keV Annihilation line, suggests that the bulk of the positron Annihilation from the Galactic center direction occurs after positronium formation in a warm environment. The inner Galaxy total Annihilation Radiation flux intensities of ~10.6 × 10-3 to ~13.7 × 10-3 cm-2 s-1 implied by the fitted R1/4 ellipsoid plus exponential disk model (narrow and broad disks, respectively) are in agreement with intensities implied by the 511 keV line flux observed by the broad-field SMM instrument. The double-Gaussian plus CO disk model gives similar agreement if a broad (~12° FWHM) disk component is assumed.
-
OSSE observations of galactic 511 keV Annihilation Radiation
1993Co-Authors: W R Purcell, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, J D Kurfess, G V JungAbstract:The Oriented Scintillation spectrometer Experiment (OSSE) on the Compton Gamma‐Ray Observatory has performed numerous observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron Annihilation Radiation and to search for time variability of the emission. These observations show conclusive evidence for a narrow 511 keV line and positronium continuum. For the first OSSE galactic center observation, the fitted 511 keV line flux was (2.3±0.3)×10−4 γ cm−2 s−1 and the positronium continuum flux was (8.8±0.7)×10−4 γ cm−2 s−1, corresponding to a positronium fraction (0.96±0.04). The quoted uncertainty in the positronium flux does not include the effect of the underlying continuum model on the fitted positronium flux. No significant time variability of the line flux has been observed; the 3σ upper limit to daily variations from the mean is 3×10−4 γ cm−2 s−1. The galactic distribution of the 511 keV line emission is found to be most consistent with a 2‐compon...
-
osse observations of galactic 511 kev positron Annihilation Radiation initial phase 1 results
The Astrophysical Journal, 1993Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:Abstract : The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory (GRO) has performed numerous observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron Annihilation Radiation and to search for time variability of the emission; the initial 511 keV line fluxes for the observations performed during the first 18 months of the GRO mission are presented. The 511 keV line flux for a typical galactic center observation is (2:5 plus or minus 0:3) x 10(exp -1) gamma sq cm s(exp -1), where the quoted uncertainty represents the 1 sigma statistical uncertainty. No statistically significant time variability of the line flux has been observed; the 3 sigma upper linit to daily variations from the mean is 3 x 10(exp -4) gamma sq cm s(exp -1). The distribution of galactic 511 keV positron Annihilation Radiation implied by the OSSE observations is discussed and compared with observations by other instruments.
-
limits on a variable source of 511 kev Annihilation Radiation near the galactic center
The Astrophysical Journal, 1990Co-Authors: G H Share, M D Leising, D C Messina, W R PurcellAbstract:The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission satellite (SMM) has observed a strong Galactic source of 511 keV Annihilation Radiation from its launch in 1980 to its reentry in 1989. These observations are consistent with an extended source having an intensity of about 0.002 gamma/sq cm/s averaged over the central radian of Galactic longitude. These data are searched for evidence of the variable Galactic center source of 511 keV line Radiation which was reported to have reappeared in 1988 by Leventhal et al. The SMM data are consistent with, but do not require, a compact source emitting a time-averaged flux of about 0.0004 gamma/sq cm/s during about 3 month transits in 1987 and 1988; they are inconsistent with a compact source flux in excess of 0.0008 gamma/sq cm/s for each year. 14 refs.
R L Kinzer - One of the best experts on this subject based on the ideXlab platform.
-
Supernovae and positron Annihilation Radiation
New Astronomy Reviews, 2020Co-Authors: P A Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron Annihilation Radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic Annihilation Radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the Annihilation Radiation studies.Comment: 7 pages, accepted for publication in New Astronomy Reviews (Astronomy with Radioactivites III
-
The distribution of galactic 511 keV positron Annihilation Radiation
AIP Conference Proceedings, 2008Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:The Oriental Scintillation Spectrometer Experiment (OSSE) on NASA’s Compton Gamma‐Ray Observatory has completed numerous observations of the Galactic plane and Galactic center region. A principle objective of these observations was to measure the distribution of the Galactic positron Annihilation Radiation. Most of these observations provided positive detections of the narrow 511 keV Annihilation line. These data were fitted using several diffuse distribution models representing various populations of progenitor objects. The only model investigated which is not rejected is a two‐component distribution consisting of spheroidal and disk components; all other models investigated can be rejected at the ≳4.5σ confidence level. The size of the spheroidal component is found to be
-
supernovae and positron Annihilation Radiation
New Astronomy Reviews, 2002Co-Authors: P A Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron Annihilation Radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic Annihilation Radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the Annihilation Radiation studies.
-
comparative studies of line and continuum positron Annihilation Radiation
arXiv: Astrophysics, 2001Co-Authors: P Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Positron Annihilation Radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron Annihilation Radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual Annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis.
-
positron Annihilation Radiation from the inner galaxy
The Astrophysical Journal, 2001Co-Authors: R L Kinzer, P A Milne, J D Kurfess, M S Strickman, W N Johnson, W R PurcellAbstract:The OSSE instrument on the Compton Gamma Ray Observatory (CGRO) was used to measure the one-dimensional latitudinal and longitudinal distributions of positron Annihilation Radiation (Annihilation line and positronium continuum components) along the inner Galactic ridge. Intensity measurements near the Galactic center (differential relative to background fields offset by 9°-12°) show a symmetrical and spatially narrow bulge around the center (effective FWHMs of 49 ± 07 in Galactic latitude and 63 ± 15 in longitude) with significant disk contributions to at least 35° in longitude. The latitude width of the Galactic plane emission away from the Galactic center is only weakly constrained in the current analysis. The longitudinal distribution is well fitted by either a model comprising a narrow (~63 FWHM ) Gaussian bulge plus ~35° FWHM Gaussian and CO-like disk components, or by a center-truncated R1/4 spheroid plus exponential disk model. For the latter model, the observed narrow latitudinal distribution near the Galactic center suggests that the bulge is ellipsoidal, although the fits are consistent with a spherical bulge as well. The positronium fraction estimate from the Galactic center direction is 0.93 ± 0.04. This, combined with the existing narrow line width measurements for the 511 keV Annihilation line, suggests that the bulk of the positron Annihilation from the Galactic center direction occurs after positronium formation in a warm environment. The inner Galaxy total Annihilation Radiation flux intensities of ~10.6 × 10-3 to ~13.7 × 10-3 cm-2 s-1 implied by the fitted R1/4 ellipsoid plus exponential disk model (narrow and broad disks, respectively) are in agreement with intensities implied by the 511 keV line flux observed by the broad-field SMM instrument. The double-Gaussian plus CO disk model gives similar agreement if a broad (~12° FWHM) disk component is assumed.
P. Von Ballmoos - One of the best experts on this subject based on the ideXlab platform.
-
INTEGRAL/IBIS search for e - e + Annihilation Radiation from the galactic center region
Advances in Space Research, 2020Co-Authors: G De Cesare, V. Lonjou, F Capitanio, M Del Santo, L Natalucci, P Ubertini, Angela Bazzano, P. Von BallmoosAbstract:Abstract Electron–positron Annihilation Radiation from the Galactic Center Region has been detected since the seventies, but its astrophysical origin is still a topic of a scientific debate. We have analyzed data of the gamma-ray imager IBIS/ISGRI onboard of ESA’s INTEGRAL platform in the e − e + line. During the first year of the missions Galactic Center Deep Exposure no evidence for point sources at 511 keV has been found in the ISGRI data; the 2 σ upper limit for resolved single point sources is estimated to be 1.6 × 10 −4 ph cm −2 s −1 .
-
integral ibis search for e e Annihilation Radiation from the galactic center region
Advances in Space Research, 2006Co-Authors: G De Cesare, V. Lonjou, A Bazzano, F Capitanio, M Del Santo, L Natalucci, P Ubertini, P. Von BallmoosAbstract:Abstract Electron–positron Annihilation Radiation from the Galactic Center Region has been detected since the seventies, but its astrophysical origin is still a topic of a scientific debate. We have analyzed data of the gamma-ray imager IBIS/ISGRI onboard of ESA’s INTEGRAL platform in the e − e + line. During the first year of the missions Galactic Center Deep Exposure no evidence for point sources at 511 keV has been found in the ISGRI data; the 2 σ upper limit for resolved single point sources is estimated to be 1.6 × 10 −4 ph cm −2 s −1 .
-
integral spi limits on electron positron Annihilation Radiation from the galactic plane
The Astrophysical Journal, 2005Co-Authors: Bonnard J. Teegarden, V. Lonjou, G. Weidenspointner, J. Knödlseder, P. Jean, P. Von Ballmoos, J. P. Roques, K Watanabe, G Skinner, A BazzanoAbstract:The center of our Galaxy is a known strong source of electron-positron 511 keV Annihilation Radiation. Thus far, however, there have been no reliable detections of Annihilation Radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (International Gamma-Ray Astrophysics Laboratory) mission, launched in 2002 October, is the detailed study of this Radiation. The Spectrometer on INTEGRAL (SPI) is a high-resolution, coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution, and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic plane. No positive Annihilation flux was detected outside of the central region ( l > 40°) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511 keV flux.
-
SPI observations of positron Annihilation Radiation from the 4th galactic quadrant: Spectroscopy
arXiv: Astrophysics, 2004Co-Authors: V. Lonjou, G. Weidenspointner, J. Knödlseder, P. Jean, Marc Allain, P. Von Ballmoos, M. J. Harris, J. P. Roques, G. K. Skinner, Bonnard J. TeegardenAbstract:The status of the analysis of the electron/positron Annihilation Radiation performed by INTEGRAL/SPI in the 4th GALACTIC QUADRANT is reported. We use data from the first two Galactic Center Deep Exposures (GCDE) and from the Galactic Plane Scans (GPS). The analysis presented here is focused on the spectroscopic aspects of the electron/positron Annihilation Radiation. Background substraction and model fitting methods are described, and the parameters of the 511 keV line (flux, energy, and width) are deduced.
-
SPI observations of positron Annihilation Radiation from the 4th galactic quadrant: sky distribution
arXiv: Astrophysics, 2004Co-Authors: G. Weidenspointner, V. Lonjou, P. Jean, Marc Allain, P. Von Ballmoos, M. J. Harris, G. K. Skinner, J. Knoedlseder, G. Vedrenne, Bonnard J. TeegardenAbstract:During its first year in orbit the INTEGRAL observatory performed deep exposures of the Galactic Center region and scanning observations of the Galactic plane. We report on the status of our analysis of the positron Annihilation Radiation from the 4th Galactic quadrant with the spectrometer SPI, focusing on the sky distribution of the 511 keV line emission. The analysis methods are described; current constraints and limits on the Galactic bulge emission and the bulge-to-disk ratio are presented.
J D Kurfess - One of the best experts on this subject based on the ideXlab platform.
-
Galactic positron Annihilation Radiation
Advances in Space Research, 2020Co-Authors: J D KurfessAbstract:Abstract Positron Annihilation Radiation from the galactic center region was first detected nearly 30 years ago. Several potential sources may contribute to this emission, including: (1) β + -decay of nuclei produced in explosive objects (supernovae and novae); (2) γ-γ pair production associated with the accretion of matter onto galactic black holes; (3) positrons produced in pair cascades in pulsar magnetospheres; (4) β + -decay of radioactive nuclei synthesized in Wolf-Rayet and AGB stars and carried in their stellar winds; and (5) positrons produced by interactions of cosmic rays with the interstellar medium. Early evidence for variability of the galactic center emission suggested that one or more discrete sources dominated the emission. However, more recent SMM /GRS, COMPTON /OSSE and WIND /TGRS results indicate that the dominant emission is steady and of diffuse origin. Transient positron production associated with galactic black hole candidates has been reported; however, there are limits for at least one of these events which are in disagreement with the reports. The OSSE instrument has provided the first maps of the emission, and the discovery of a surprising excess at positive galactic latitudes above the center of the Galaxy. The history of these observations is discussed, along with the latest data available from OSSE and TGRS. We also discuss the implications of the observations on our understanding of galactic nucleosynthesis, galactic distributions of supernovae, and the study of the interstellar medium.
-
Supernovae and positron Annihilation Radiation
New Astronomy Reviews, 2020Co-Authors: P A Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron Annihilation Radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic Annihilation Radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the Annihilation Radiation studies.Comment: 7 pages, accepted for publication in New Astronomy Reviews (Astronomy with Radioactivites III
-
The distribution of galactic 511 keV positron Annihilation Radiation
AIP Conference Proceedings, 2008Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:The Oriental Scintillation Spectrometer Experiment (OSSE) on NASA’s Compton Gamma‐Ray Observatory has completed numerous observations of the Galactic plane and Galactic center region. A principle objective of these observations was to measure the distribution of the Galactic positron Annihilation Radiation. Most of these observations provided positive detections of the narrow 511 keV Annihilation line. These data were fitted using several diffuse distribution models representing various populations of progenitor objects. The only model investigated which is not rejected is a two‐component distribution consisting of spheroidal and disk components; all other models investigated can be rejected at the ≳4.5σ confidence level. The size of the spheroidal component is found to be
-
supernovae and positron Annihilation Radiation
New Astronomy Reviews, 2002Co-Authors: P A Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron Annihilation Radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic Annihilation Radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the Annihilation Radiation studies.
-
comparative studies of line and continuum positron Annihilation Radiation
arXiv: Astrophysics, 2001Co-Authors: P Milne, J D Kurfess, R L Kinzer, M D LeisingAbstract:Positron Annihilation Radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron Annihilation Radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual Annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis.
G V Jung - One of the best experts on this subject based on the ideXlab platform.
-
The distribution of galactic 511 keV positron Annihilation Radiation
AIP Conference Proceedings, 2008Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:The Oriental Scintillation Spectrometer Experiment (OSSE) on NASA’s Compton Gamma‐Ray Observatory has completed numerous observations of the Galactic plane and Galactic center region. A principle objective of these observations was to measure the distribution of the Galactic positron Annihilation Radiation. Most of these observations provided positive detections of the narrow 511 keV Annihilation line. These data were fitted using several diffuse distribution models representing various populations of progenitor objects. The only model investigated which is not rejected is a two‐component distribution consisting of spheroidal and disk components; all other models investigated can be rejected at the ≳4.5σ confidence level. The size of the spheroidal component is found to be
-
OSSE observations of galactic 511 keV Annihilation Radiation
1993Co-Authors: W R Purcell, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, J D Kurfess, G V JungAbstract:The Oriented Scintillation spectrometer Experiment (OSSE) on the Compton Gamma‐Ray Observatory has performed numerous observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron Annihilation Radiation and to search for time variability of the emission. These observations show conclusive evidence for a narrow 511 keV line and positronium continuum. For the first OSSE galactic center observation, the fitted 511 keV line flux was (2.3±0.3)×10−4 γ cm−2 s−1 and the positronium continuum flux was (8.8±0.7)×10−4 γ cm−2 s−1, corresponding to a positronium fraction (0.96±0.04). The quoted uncertainty in the positronium flux does not include the effect of the underlying continuum model on the fitted positronium flux. No significant time variability of the line flux has been observed; the 3σ upper limit to daily variations from the mean is 3×10−4 γ cm−2 s−1. The galactic distribution of the 511 keV line emission is found to be most consistent with a 2‐compon...
-
osse observations of galactic 511 kev positron Annihilation Radiation initial phase 1 results
The Astrophysical Journal, 1993Co-Authors: W R Purcell, J D Kurfess, R L Kinzer, M S Strickman, W N Johnson, D A Grabelsky, M P Ulmer, G V JungAbstract:Abstract : The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory (GRO) has performed numerous observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron Annihilation Radiation and to search for time variability of the emission; the initial 511 keV line fluxes for the observations performed during the first 18 months of the GRO mission are presented. The 511 keV line flux for a typical galactic center observation is (2:5 plus or minus 0:3) x 10(exp -1) gamma sq cm s(exp -1), where the quoted uncertainty represents the 1 sigma statistical uncertainty. No statistically significant time variability of the line flux has been observed; the 3 sigma upper linit to daily variations from the mean is 3 x 10(exp -4) gamma sq cm s(exp -1). The distribution of galactic 511 keV positron Annihilation Radiation implied by the OSSE observations is discussed and compared with observations by other instruments.