ABSTRACT

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ABSTRACT: Recently Narayan et al. (1998) have used an advection dominated accretion flow (ADAF) model to explain the low luminosity and spectrum from Sgr A*. This model explains the millimeter to hard X-ray spectrum quite well, but has had difficulty in agreeing with the low energy radio observations. An essential element of the model is that the thermal electrons must co-exist with hot (nearly virial) protons throughout the flow. Until now, this two temperature nature has been little more than theoretical speculation. We show that an emission process associated with the protons naturally resolves the observed discrepancy and low radio energies. In particular, the hot protons produce charged pions which subsequently decay into electrons and positrons. These high energy particles interact with the local magnetic fields to produce synchrotron radiation which naturally reproduces the observed spectral break at ~ 86 GHz as well as the low energy radio spectrum. No fine tuning of the model is allowed. This provides observational support for both a two temperature plasma, and a power-law energy distribution of protons. Further, it gives increasing support to the idea that Sgr A* most probably accretes via an ADAF.