OSSE Mapping of Positron Annihilation Radiation
During eight years of operation the OSSE instrument on-board CGRO has
observed sources in many regions of the sky,
primarily near the Galactic Center and along the Galactic Plane.
From these individual observations, Purcell et al. (1993,1997)
created a large dataset
of fitted 511 keV line fluxes, and mapped the
Galactic Center region. These were the first maps of
galactic positron annihilation radiation. That dataset has been
augmented with additional data, both recent and archival, and re-analyzed
to improve the spectral fitting. The improved spectral fitting has
permitted the estimation of the positronium continuum emission (the
fitted 511 keV line is robust relative to spectral modelling).
The mapped region has been extended to include the entire Galactic Plane,
as well as the Virgo and LMC/SMC regions.
Maps of both components of positron annihilation radiation have been
generated, and combined to form maps of positron annihilation radiation
which cover ~ 65% of the sky. These are the first maps ever produced
of positronium continuum emission, and the most extensive maps of 511 keV
line emission. The central component of the 511 keV map
remains the Galactic Center region, the current maps show improved
definition due to additional exposure.
Utilizing simulated maps for comparison, the astrophysical
implications of these maps will be discussed. Particular issues
addressed will be the shape of the bulge and disk emission,
the status of the ``annihilation fountain", the
evidence for emission away from the Galactic Plane, and the spatial
variation of the positronium fraction.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.