HIGH-FREQUENCY MEASUREMENTS OF THE SPECTRUM OF SAGITTARIUS A-ASTERISK

We report near-simultaneous interferometric measurements of the spectr um of Sagittarius A over the 5-354 GHz range and single-dish observat ions that have yielded the first detection of Sgr A at 850 GHz. We co nfirm that Sgr A's spectrum rises more steeply at short millimeter wa velengths than at centimeter wavelengths, leading to a near-millimeter /submillimeter excess that dominates its luminosity. Below 900 GHz, Sg r A's observed luminosity is 70 +/- 30 L.. A new upper limit to Sgr A 's 24.3 mu m flux, together with a compilation of other extant IR dat a, imply a far-infrared spectral turnover, which can result from eithe r an intrinsic synchrotron cutoff or excess extinction near Sgr A. If the former applies, Sgr A's total synchrotron luminosity is <10(3) L ., while in the latter case it is <3 x 10(4) L. if spherical symmetry also applies.