On the Origin of the 511 keV Emission in the Galactic Centre

Reba M. Bandyopadhyay1, Joseph Silk2, James E. Taylor3 and Thomas J. Maccarone4

(1) Department of Astronomy, 211 Bryant Space Science Centre, Gainesville, FL 32611-2055 USA
(2) Department of Astrophysics, Denys Wilkinson Building, 1 Keble Road, Oxford OX1 3RH, UK
(3) Department of Physics & Astronomy, 200 University Avenue West, Waterloo, Ontario, N2L 3G1 Canada
(4) School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK

Paper: MNRAS, 2009, vol. 392

EPrint Server: 0810.3674


Diffuse 511 keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 years. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of 70 luminous, low-mass X-ray binaries detected in the soft gamma-ray band. The X-ray band, however, is generally a more sensitive probe of X-ray binary populations. Recent X-ray surveys of the Galactic Centre have discovered a much larger population (>4000) of faint, hard X-ray point sources. We investigate the possibility that the positrons observed in the direction of the Galactic Centre originate in pair-dominated jets generated by this population of fainter accretion-powered X-ray binaries. We also consider briefly whether such sources could account for unexplained diffuse emission associated with the Galactic Centre in the microwave (the WMAP `haze') and at other wavelengths. Finally, we point out several unresolved problems in associating Galactic Centre 511 keV emission with the brightest X-ray binaries.

Preprints available from the authors at reba@astro.ufl.edu , or the raw TeX (no figures) if you click here.

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