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The Australia Telescope National Facility Colloquium
15:30-16:30 Wed 12 Jul 2006

ATNF Basement Meeting Room

Roland Crocker

(University of Adelaide)

Non-thermal Emission from the Sagittarius B GMC and the Cosmic Ray Spectrum in the Galactic Center Region - Roland Crocker Colloquium

The HESS instrument has recently observed a diffuse flux of gamma-rays in the energy range ~300 GeV - 10 TeV emanating from a large solid angle (~2 deg by 1 deg) around the Galactic centre (GC). Of particular interest, the HESS observations reveal gamma ray emission from the Sagittarius B Giant Molecular Cloud which is located at around 100 pc from the actual GC. In general, over the entire field of observation the gamma-ray emission is correlated with the ambient gas density through the GC region suggesting that the gamma rays ultimately originate in hadronic interactions between a population of cosmic rays (CRs) pervading the region and ambient matter. Prompted by this, using the ATCA, we have made detailed radio observations of Sgr B to see whether we can detect the non-thermal signature of synchrotron emission from the expected ambient secondary electrons and positrons (created in the same hadronic interactions between the GC CR population and ambient gas that
supply the observed gamma rays). Combining our observations with data
obtained by the VLA at 90 and 400 cm, we have tentatively uncovered non-thermal emission at the expected level, though a definitive claim cannot yet be made given the strong thermal emission by HII regions within Sgr B. We discuss the implications of our observations and analysis for the CR spectrum in the GC region and, more broadly, for the somewhat mysterious FIR-RC correlation.

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