An Apparent Anomalous Diffuse gamma-ray emission feature, and
its Possible Association with the the worm GW18.5+2.8
D. D. Dixon
D. H. Hartmann
We present results of an analysis of EGRET data which
indicate the presence of a possible anomalous diffuse
emission feature. The analysis method nonparametrically
estimates statistically significant residuals in a Poisson
dataset relative to a given null hypothesis. Here, our null
hypothesis consisted of a model for Galactic diffuse
gamma-ray emission, the estimated isotropic gamma-ray
background, a symmetric halo component, and the point
sources from the Lamb and Macomb GeV EGRET source catalog.
The resultant residual shows an apparently diffuse feature
emanating northward from the Galactic plane in the region
l ~ 15° - 21°. Examination of COMPTEL skymaps indicate a
very bright but unidentified MeV source which coincides with
the footpoint of the GeV feature. Further, the location and
longitudinal extent of this feature is highly coincident
with that of the ``worm'' GW 18.5+2.8 (Heiles, Reach, and
Koo 1996, ApJ, 466, 191), a large radio feature which
includes the Stockert Chimney. A powerful HII region, M16,
lies at the base of GW 18.5+2.8. We discuss the possibility
that cosmic-rays from massive stellar processes may be
responsible for the gamma-ray emission.
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On 16 Jul 1999, 09:19.