SMM detection of diffuse Galactic 511 keV annihilation radiation

Share, G. H.; Kinzer, R. L.; Kurfess, J. D.; Messina, D. C.; Purcell, W. R.; Chupp, E. L.; Forrest, D. J.; Reppin, C.

doi:10.1086/166130

Cited by 72 publications

(40 citation statements)

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“…Following early reports of a line near this energy, the first high resolution measurements (Leventhal et al 1978) established its identification as positron annihilation. Early indications of variability were later shown to have been due to comparing measurements of extended emission made with instruments having different fields of view (Albernhe et al 1981;Leventhal et al 1986;Share et al 1988).…”

Section: Introductionmentioning

confidence: 99%

Gamma-ray spectroscopy of positron annihilation in the Milky Way

Siegert

Diehl

Khachatryan

et al. 2016

A&A

148

246

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Context. The annihilation of positrons in the Galaxy's interstellar medium produces characteristic gamma-rays with a line at 511 keV. This gamma-ray emission has been observed with the spectrometer SPI on ESA's INTEGRAL observatory, confirming a puzzling morphology with bright emission from an extended bulge-like region, while emission from the disk is faint. Most known or plausible sources of positrons are, however, believed to be distributed throughout the disk of the Milky Way. Aims. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge using data with an exposure that has doubled since earlier reports. Methods. We exploit high-resolution gamma-ray spectroscopy with SPI on INTEGRAL based on a new instrumental background method and detailed multi-component sky model fitting. Results. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures, altogether at 58σ significance in the 511 keV line. The total Galactic 511 keV line intensity amounts to (2.74 ± 0.25) × 10 −3 ph cm −2 s −1 for our assumed model of the spatial distribution. We derive spectra for the bulge and disk, and a central source modelled as pointlike and at the position of Sgr A*, and discuss spectral differences. The bulge (56σ) shows a 511 keV line intensity of (0.96 ± 0.07) × 10 −3 ph cm −2 s −1 together with ortho-positronium continuum equivalent to a positronium fraction of (1.080 ± 0.029). The twodimensional Gaussian that represents the disk emission (12σ) has an extent of 60 +10 −5 degrees in longitude and a rather large latitudinal extent of 10.5 +2.5 −1.5 degrees; the line intensity is (1.66 ± 0.35)×10 −3 ph cm −2 s −1 with a marginal detection of the annihilation continuum and an overall diffuse Galactic continuum of (5.85 ± 1.05) × 10 −5 ph cm −2 s −1 keV −1 at 511 keV. The disk shows no flux asymmetry between positive and negative longitudes, although spectral details differ. The flux ratio between bulge and disk is (0.58 ± 0.13). The central source (5σ) has an intensity of (0.80 ± 0.19) × 10 −4 ph cm −2 s −1 .

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Section: Introductionmentioning

confidence: 99%

Gamma-ray spectroscopy of positron annihilation in the Milky Way

Siegert

Diehl

Khachatryan

et al. 2016

A&A

148

246

View full text Add to dashboard Cite

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“…uum (e.g., Leventhal, MacCallum, & Stang 1978 ;Riegler et al 1985 ;Harris et al 1990 ;Gehrels et al 1991 ;Slassi et al 1991 ;Smith et al 1993 ;Mahoney, Ling, & Wheaton 1993 ;Kinzer et al 1996Kinzer et al , 1999 ; (3) a 511 keV positron annihilation line (e.g., Johnson, Harnden, & Haymes 1972 ;Leventhal et al 1978 ;Riegler et al 1981 ;Share et al 1988 ;Gehrels et al 1991 ;Slassi et al 1991 ;Purcell et al 1993Purcell et al , 1996Kinzer et al 1996Kinzer et al , 1999 ; (4) a 1.809 MeV 26Al line (e.g., Mahoney et al 1984 ;Share et al 1985 ;Diehl et al 1995) ; and (5) a component resulting from cosmic rays interacting with the interstellar gas and photon Ðelds (e.g., Harris et al 1990 ;Bloemen et al 1994Bloemen et al , 1997Strong et al 1994Strong et al , 1996.…”

Section: Introductionmentioning

confidence: 99%

Gamma‐Ray Emission from the Inner Galactic Ridge

Kinzer

Purcell

Kurfess

1999

ApJ

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We present measurements of the 0.05È10 MeV gamma-ray spectra as a function of longitude from the inner Galactic ridge using the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory. The di †erential continuum emission relative to intensities at^10¡ Galactic latitude appears to be a composite of at least three independent components : a soft low-energy component with a broad longitude distribution and with spectra well approximated by an exponentially absorbed power law ; a hard component with a similarly broad longitude distribution modeled by a power law from D200 keV to 10 MeV with photon index D[1.75 ; and strong positron annihilation line and continuum contributions observed toward the center with intensities that decrease rapidly with longitude distance from the center. Although OSSE cannot distinguish between a simple one-component latitude distribution and a more complicated one with, for example, broad and narrow latitude components, an "" e †ective ÏÏ 5¡È6¡ FWHM Gaussian latitude width gives a spectrum and intensity for the power-law component that agrees with extrapolations of measurements at higher energies using a cosmic-ray interaction model. However, the latitude distribution of the emission is not well measured. Near the Galactic center, bright variable sources contribute signiÐcantly to the low-energy spectrum. When account is taken of these variable-source contributions, both the soft low-energy and hard powerlaw components show a consistent longitude distribution that follows the Galactic matter distribution as evidenced by the Galactic CO distribution. These results, in conjunction with previous measurements, provide new information for determining the Galactic cosmic-ray electron spectrum at lower energies.

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“…Early measurements ( Riegler et al 1981;Paciesas et al 1982;Leventhal et al 1982Leventhal et al , 1986 suggested that the annihilation radiation was timevariable. However, more extensive later observations showed no evidence of variability (Share et al 1988;Gehrels et al 1991;Leventhal et al 1993;Mahoney et al 1994;Teegarden et al 1996;Purcell et al 1997;Harris et al 1998). The current consensus favors the latter conclusion.…”

Section: Introductionmentioning

confidence: 96%

INTEGRALSPI Limits on Electron‐Positron Annihilation Radiation from the Galactic Plane

Teegarden¹,

Watanabe²,

Jean³

et al. 2005

ApJ

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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 highresolution, 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 (jl j> 40 ) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511 keV flux.

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SMM detection of diffuse Galactic 511 keV annihilation radiation

Cited by 72 publications

References 0 publications

Gamma-ray spectroscopy of positron annihilation in the Milky Way

Gamma-ray spectroscopy of positron annihilation in the Milky Way

Gamma‐Ray Emission from the Inner Galactic Ridge

INTEGRALSPI Limits on Electron‐Positron Annihilation Radiation from the Galactic Plane

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