The 511 keV emission from positron annihilation in the Galaxy

Journal Article · Fri Jul 01 00:00:00 EDT 2011 · Reviews of Modern Physics

DOI:https://doi.org/10.1103/REVMODPHYS.83.1001· OSTI ID:22038720

Prantzos, N; Boehm, C; Bykov, A M; Diehl, R; Ferriere, K; Guessoum, N; Jean, P; Knoedlseder, J; Marcowith, A; Moskalenko, I V; Strong, A; Weidenspointner, G ^[1]

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1. CNRS, UMR7095, UMPC and Institut d'Astrophysique de Paris, F-75014, Paris (France) and LAPP, 9 Chemin de Bellevue, BP 110 F-74941 Annecy-le-Vieux (France)

The first {gamma}-ray line originating from outside the Solar System that was ever detected is the 511 keV emission from positron annihilation in the Galaxy. Despite 30 years of intense theoretical and observational investigation, the main sources of positrons have not been identified up to now. Observations in the 1990s with OSSE/CGRO (Oriented Scintillation Spectrometer Experiment on GRO satellite/Compton Gamma Ray Observatory) showed that the emission is strongly concentrated toward the Galactic bulge. In the 2000s, the spectrometer SPI aboard the European Space Agency's (ESA) International Gamma Ray Astrophysics Laboratory (INTEGRAL) allowed scientists to measure that emission across the entire Galaxy, revealing that the bulge-to-disk luminosity ratio is larger than observed at any other wavelength. This mapping prompted a number of novel explanations, including rather ''exotic'' ones (e.g., dark matter annihilation). However, conventional astrophysical sources, such as type Ia supernovae, microquasars, or x-ray binaries, are still plausible candidates for a large fraction of the observed total 511 keV emission of the bulge. A closer study of the subject reveals new layers of complexity, since positrons may propagate far away from their production sites, making it difficult to infer the underlying source distribution from the observed map of 511 keV emission. However, in contrast to the rather well-understood propagation of high-energy (>GeV) particles of Galactic cosmic rays, understanding the propagation of low-energy ({approx}MeV) positrons in the turbulent, magnetized interstellar medium still remains a formidable challenge. The spectral and imaging properties of the observed 511 keV emission are reviewed and candidate positron sources and models of positron propagation in the Galaxy are critically discussed.

• OSTI ID: 22038720
• Journal Information: Reviews of Modern Physics, Vol. 83, Issue 3; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6861
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANNIHILATION
ASTROPHYSICS
COSMIC RADIATION
DISTRIBUTION
EMISSION
GEV RANGE
INTEGRALS
KEV RANGE
LUMINOSITY
MAPPING
NONLUMINOUS MATTER
PARTICLES
POSITRON SOURCES
POSITRONS
SATELLITES
SCINTILLATIONS
SPECTROMETERS
SUPERNOVAE
WAVELENGTHS
X RADIATION