Mathematics – Probability
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000head....5.0210b&link_type=abstract
American Astronomical Society, HEAD Meeting #5, #02.10; Bulletin of the American Astronomical Society, Vol. 32, p.1184
Mathematics
Probability
Scientific paper
X-ray emission has been detected from Sgr A* for the first time in a 50-ks Chandra observation with the ACIS-I instrument. The newly discovered X-ray source, CXO J174540.0-290027, is coincident with the radio position of Sgr A* to within 0.35″ , corresponding to a maximum projected distance of 16 light-days for an assumed distance to the center of our Galaxy of 8.0 kpc. CXO J174540.0-290027 is the third brightest X-ray source in the entire 17' x 17' field of view and the second brightest heavily absorbed source. Since the brightest absorbed source lies ≈ 0.5′ from Sgr A*, the probability of detecting an absorbed source by random chance that is as bright or brighter than the Sgr A* candidate and that lies within 0.35″ of the radio position is about 3 x 10-4. The best-fit absorbed power-law model has a photon index Γ ≈ 2.7 (N(E) E-Γ ) and a column density NH ≈ 1 x 1023\ cm-2. The measured (absorbed) flux in the 2--10 keV passband is ≈ 1x 10-13\ ergs\ cm-2\ s-1, and the absorption-corrected luminosity is ≈ 2 x 1033\ ergs\ s-1. The spectrum is equally well fit by an absorbed thermal bremsstrahlung model with kT ≈ 4\ keV and NH ≈ 8 x 1022\ cm-2. Implications of the measured flux and spectrum for ADAF, CDAF, jet-disk, and other emission models are discussed. Comparison of the X-ray spectral shape and LX/L_R ratio of Sgr A* to a sample of LLAGN indicates that their high-energy emission mechanisms are significantly different. This research was supported by NASA grant NAS8-38252.
Baganoff Frederick Keith
Bautz Mark W.
Brandt Wiliam N.
Cui Wei-Wei
Doty John P.
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