TY - JOUR
KW - Space and Planetary Science
KW - Astronomy and Astrophysics
AU - Geoffrey Bower
AU - Jason Dexter
AU - Keiichi Asada
AU - Christiaan Brinkerink
AU - Heino Falcke
AU - Paul Ho
AU - Makoto Inoue
AU - Sera Markoff
AU - Daniel Marrone
AU - Satoki Matsushita
AU - Monika Mościbrodzka
AU - Masanori Nakamura
AU - Alison Peck
AU - Ramprasad Rao
AB - We present Atacama Large Millimeter/submillimeter Array (ALMA) observations at 233, 678, and 870 GHz of the Galactic Center black hole, Sagittarius A*. These observations reveal a flat spectrum over this frequency range with spectral index alpha approximate to -0.3, where the flux density S proportional to nu(alpha). We model the submillimeter and far-infrared spectrum with a one-zone synchrotron model of thermal electrons. We infer electron densities n = (2-5) x 10(6) cm(-3), electron temperatures T-e = (1-3) x 10(11 )K, and magnetic field strength B = 10-50 G. The parameter range can be further constrained using the observed quiescent X-ray luminosity. The flat submillimeter spectrum results in a high electron temperature and implies that the emitting electrons are efficiently heated. We also find that the emission is most likely optically thin at 233 GHz. These results indicate that millimeter and submillimeter wavelength very long baseline interferometry of Sgr A* including those of the Event Horizon Telescope should see a transparent emission region down to event horizon scales.
BT - The Astrophysical Journal
DA - 2020-08
DO - 10.3847/2041-8213/ab3397
IS - 1
N2 - We present Atacama Large Millimeter/submillimeter Array (ALMA) observations at 233, 678, and 870 GHz of the Galactic Center black hole, Sagittarius A*. These observations reveal a flat spectrum over this frequency range with spectral index alpha approximate to -0.3, where the flux density S proportional to nu(alpha). We model the submillimeter and far-infrared spectrum with a one-zone synchrotron model of thermal electrons. We infer electron densities n = (2-5) x 10(6) cm(-3), electron temperatures T-e = (1-3) x 10(11 )K, and magnetic field strength B = 10-50 G. The parameter range can be further constrained using the observed quiescent X-ray luminosity. The flat submillimeter spectrum results in a high electron temperature and implies that the emitting electrons are efficiently heated. We also find that the emission is most likely optically thin at 233 GHz. These results indicate that millimeter and submillimeter wavelength very long baseline interferometry of Sgr A* including those of the Event Horizon Telescope should see a transparent emission region down to event horizon scales.
PB - American Astronomical Society
PY - 2019
EP - L2
T2 - The Astrophysical Journal
TI - ALMA Observations of the Terahertz Spectrum of Sagittarius A*
VL - 881
SN - 2041-8213
ER -