A Maximum Entropy Map of the 511 keV Positron Annihilation Line Emission Distribution Near the Galactic Center

L.X. Cheng(1), M. Leventhal(1), D.M. Smith(1), W.R. Purcell(2), J. Tueller(3), A. Connors(4), D. Dixon(5), R.L. Kinzer(6), J.G. Skibo(6)

(1) Departmentof Astronomy, University of Maryland, College Park, MD 20742 (2) Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (3) Laboratory for High Energy Astrophysics, NASA/GSFC, Greenbelt, MD 20771 (4) Space Science, Morse Hall, University of New Hampshire, Durham, NH 03824 (5) University of California, Institute for Geophysics and Planetary Physics,Riverside, CA 92521 (6) Code 7650, Naval Research Laboratory, Washington, DC 20375

Paper: submitted to ApJ Letters

Abstract:

We have applied the Maximum Entropy Method to a large data set which was constructed based on CGRO/OSSE, SMM, TGRS, GRIS, HEXAGONE and FIGARO observational results of the Galactic Center 511 keV annihilation radiation to produce a Maximum Entropy map of the 511 keV line emission distribution. This map suggests that the 511 keV emission from this region consists of at least two components: a central bulge with a flux of 5.7 +/- 0.29*10^-4 ph cm^-2 s^-1 and a Galactic Plane component with a flux of 2.2 +/- 0.4*10^-4 ph cm^-2 s^-1. The central bulge has a centroid of l=-0.47+/-0.24, b=0.1+/-0.18 and FWHM~ 5^o. We note that the Galactic Plane component agrees in position with a strong hot spot in the Comptel map of 1.8 MeV ^26Al line emission. The 511 keV line flux difference between CGRO/OSSE and other instruments with larger field-of-view suggests the existence of an extended diffuse 511 keV emission. An interesting hot spot at l=-4^o, b=7^o with a flux of ~2*10^-4 ph cm^-2s^-1 is shown on our map. A bootstrap test indicates that the significance level of this feature is 3.5 sigma .

Preprints available from the authors at lxcheng@astro.umd.edu .

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