New Clues on the Origin of Galactic Positrons
Abstract
The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us with an unprecedented view of positron annihilation in our Galaxy. The first all-sky maps in the 511 keV annihilation line (Knoedlseder et al. 2005) and in the positronium continuum (Weidenspointner et al. 2006) showed a surprisingly high concentration of annihilation radiation in the central region of our Galaxy. In this region, positrons annihilate in a warm interstellar medium, as demonstrated by high-resolution spectroscopy (Churazov et al. 2005, Jean et al. 2006). By now, about twice as many INTEGRAL observations are available, offering new clues on the origin of Galactic positrons. The augmented data set allows us to perform a detailed study of the spatial (and spectral) characteristics of the dominant emission from the central region of the Galaxy and to set increasingly stringent limits on the faint emissions from the Galactic disk and potentially from the Galactic halo. We discuss the implications of the observed large-scale distribution of annihilation emission on the origin of positrons. Our results emphasize the importance of understanding the propagation of positrons when relating the observed sky distribution of 511 keV line emission to the Galactic distribution of potential positron sources.
- Publication:
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AAS/High Energy Astrophysics Division #9
- Pub Date:
- September 2006
- Bibcode:
- 2006HEAD....9.2107W