New Limits on Diffuse Galactic Emission of Gamma Rays with Energies above 10$^{14}$ eV
Session 65 -- The Galaxy and Galactic ISM
Oral presentation, Thursday, 2, 1994, 10:00-11:30

## [65.01] New Limits on Diffuse Galactic Emission of Gamma Rays with Energies above 10$^{14}$ eV

\newbox\grsign \setbox\grsign=\hbox{$>$} \newdimen\grdimen \grdimen=\ht\grsign \newbox\simlessbox \newbox\simgreatbox \setbox\simgreatbox=\hbox{\raise.5ex\hbox{$>$} \llap {\lower.5ex\hbox{$\sim$}}} \ht1=\grdimen\dp1=0pt \setbox\simlessbox=\hbox{\raise.5ex\hbox{$<$} \llap {\lower.5ex\hbox{$\sim$}}} \ht2=\grdimen\dp2=0pt \def\simgreat{\mathrel{\copy\simgreatbox}} \def\simless{\mathrel{\copy\simlessbox}} \newbox\simppropto \setbox\simppropto=\hbox{\raise.5ex\hbox{$\sim$} \llap {\lower.5ex\hbox{$\propto$}}} \ht2=\grdimen\dp2=0pt \def\simpropto{\mathrel{\copy\simppropto}} C.E.Covault, A.Borione, J.W.Cronin, B.E.Fick, L.F.Fortson, K.G.Gibbs,B.J.Newport, T.A.McKay, R.A.Ong, L.J Rosenberg (EFI,U of Chicago), M.Catanese, K.D.Green, A.Kennedy, J.Matthews, D.Nitz, D.Sinclair, J.C. van der Velde (U of Michigan), D.B.Kieda (U of Utah)

The Chicago Air Shower Array (CASA) operates in coincidence with the Michigan muon array (MIA), and is sensitive to gamma rays with energies $\simgreat 100$ TeV. We describe a search for diffuse gamma ray emission from molecular cloud regions which are located within 10 degrees of the galactic plane as seen from the northern hemisphere. The emission mechanism and spatial distribution of diffuse gamma rays at 100 TeV should be similar to gamma rays detected at 100 MeV energies by the EGRET experiment aboard the Compton Gamma Ray Observatory. CASA-MIA is well suited to discriminate against hadronic background cosmic rays, based upon the muon content of air showers. We search for diffuse gamma rays by seeking an excess of muon-poor showers from the direction of candidate source regions. Current flux limits are beginning to approach predictions for diffuse emission based upon a uniform distribution of cosmic rays in the galaxy.