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2008MNRAS.390..683P - Mon. Not. R. Astron. Soc., 390, 683-692 (2008/October-3)
Interpretation of radio continuum and molecular line observations of Sgr B2: free-free and synchrotron emission, and implications for cosmic rays.
PROTHEROE R.J., OTT J., EKERS R.D., JONES D.I. and CROCKER R.M.
Abstract (from CDS):
We assemble radio-continuum data at frequencies between 330 MHz and 230 GHz. From the spectral-energy distribution, the emission appears to be thermal at all frequencies. Before using these data to constrain the predicted synchrotron flux, we first model the spectrum as free-free emission from the known ultra compact HII regions plus emission from an envelope or wind with a radial-density gradient, and obtain an excellent fit. We thus find the spectrum at all frequencies to be dominated by thermal emission, and this severely constrains the possible synchrotron emission by secondary electrons to quite low-flux levels. The absence of a significant contribution by secondary electrons is almost certainly due to multi-GeV energy cosmic rays being unable to penetrate far into giant molecular clouds. This would also explain why 100 MeV-GeV gamma-rays (from neutral pion decay or bremsstrahlung by secondary electrons) were not observed from Sgr B2 by the EGRET instrument on the Compton Gamma Ray Observatory, while TeV energy gamma-rays were observed by the High Energy Stereoscopic System (HESS), being produced by higher energy cosmic rays which more readily penetrate giant molecular clouds.
Abstract Copyright: © 2008 The Authors. Journal compilation © 2008 RAS
Journal keyword(s): radiation mechanisms: non-thermal - cosmic rays - HII regions - ISM: individual: Sgr B2 Giant Molecular Cloud - radio continuum: ISM - radio lines: ISM
Simbad objects: 9
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