150 GHz NOBA observations of the Galactic Center Arc

We have used the seven-beam 150 GHz bolometer NORA installed at the Nobeyam a 45-m telescope to map the central section of the Galactic Center Are. In addition, we mapped Sgr A, which shows Sgr A* and the thermal spiral struct ure. The results agree with previous mm-observations. South of the thermal "sickle" feature (G0.18 - 0.04) we observed three regions of enhanced emiss ion along the Are, which are located slightly offset relative to the most i ntense vertical filaments seen at low frequencies. This 150 GHz emission is observed at the apparent interacting areas of dense molecular material wit h the Are. Another structure is seen south of the molecular cloud, where th e Are's vertical filaments apparently cross a weak filamentary structure ru nning orthogonally in the direction of Sgr A. The 150 GHz results are unexp ected in view of previous 32 GHz and 43 GHz results, which indicate a fadin g of the Are towards higher frequencies. Cold dust can be ruled out as the origin of the 150 GHz emission. Synchrotron emission from quasi-monoenerget ic electrons or an electron distribution with a low-energy cut-off seems to be compatible with the available data. The coincidence of enhanced emissio n with regions of interacting molecular gas strongly suggests that high-ene rgy electrons are accelerated in those places where the magnetic field is c ompressed, and subsequently enter and illuminate the Arc.