The all-sky distribution of 511 keV electron-positron annihilation emission

By Jürgen Knödlseder, P. Jean, Vincent Lonjou, G. Weidenspointner, N. Guessoum, W. Gillard, G. Skinner, P. V. Ballmoos, G. Vedrenne, J. Roques and 4 more. 2005

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We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately 95% of the celestial sphere. 511 keV line emission is significantly detected towards the galactic bulge region and, at a very low level, from the galactic disk. The bulge emission is highly symmetric and is centred on the galactic centre with an extension of 8 deg. The emission is equally well described by models that represent the stellar bulge or halo populations. The disk morphology is only weakly constrained by the present data, being compatible with both the distribution of young and old stellar populations. The 511 keV line flux from the bulge and disk components is 1.05e-3 ph cm-2 s-1 and 0.7e-3 ph cm-2 s-1, respectively, corresponding to a bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of 0.93 this translates into annihilation rates of 1.5e43 s-1 and 3e42 s-1, respectively. The ratio of the bulge luminosity to that of the disk is in the range 3-9. We find no evidence for a point-like source in addition to the diffuse emission, down to a typical flux limit of 1e-4 ph cm-2 s-1. We also find no evidence for the positive latitude enhancement that has been reported from OSSE measurements; our 3 sigma upper flux limit for this feature is 1.5e-4 ph cm-2 s-1. The disk emission can be attributed to the beta+ decay of the radioactive species 26Al and 44Ti. The bulge emission arises from a different source which has only a weak or no disk component. We suggest that Type Ia supernovae and/or low-mass X-ray binaries are the prime candidates for the source of the galactic bulge positrons. Light dark matter annihilation could also explain the observed 511 keV bulge emission characteristics.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/be6df5b26629b5e1d582f59d9642996b2385444e

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Citations in the corpus

Gamma-ray spectroscopy of Positron Annihilation in the Milky Way (2015, background): “This led to a first all-sky image of positron annihilation gamma-rays (Knödlseder et al. 2003, 2005).”
Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge (2008, background): “These values are ∼ 10% of the positron annihilation rate ∼ 1.8× 1043 s−1 as derived from INTEGRAL observations of the 511 keV line emission (Knödlseder et al. 2005).”
The 511 keV emission from positron annihilation in the Galaxy (2010, methodology): “The first 511 keV line and positronium continuum all-sky maps have been presented by Knödlseder et al. (2005) and Weidenspointner et al. (2006), respectively, 8 based on approximately one year of SPI data (Fig.”
Dark matter direct detection signals inferred from a cosmological N-body simulation with baryons (2009, background): “The INTEGRAL 511 keV line γ-ray signal [18] can be explained by the emission of low mass X-ray binaries [28].”
Impact of dark matter decays and annihilations on reionization (2006, background): “The SPI spectrometer aboard ESA’s INTEGRAL satellite recently detected an excess in the 511 keV line emission, due to positron-electron annihilation, from the galactic bulge (Knödlseder et al. 2005).”
Characterizing Supernova Progenitors via the Metallicities of their Host Galaxies, from Poor Dwarfs to Rich Spirals (2007, background): “Besides the 1.809 MeV line from 26Al, the 0.511 MeV line from positron annihilation is poorly understood in terms of its high flux and very strong central concentration (e.g., Cassé et al. 2004;Knödlseder et al. 2005; Beacom &Yüksel 2006).”