X-ray sources and star formation activity in the Sagittarius B2 cloud observed with Chandra.
TAKAGI S.-I., MURAKAMI H. and KOYAMA K.
Abstract (from CDS):
We report the X-ray population study in the giant molecular cloud Sagittarius B2 (Sgr B2). More than a dozen X-ray cloud members (and candidates) are discovered with Chandra. Two bright X-ray sources are located near Sgr B2 Main, the most copious complex of the ultracompact H II sources. The X-ray spectra are fitted with a thin thermal plasma model of 5-10 keV temperature. The intrinsic luminosity, after correcting the absorption of ∼5x1023Hcm–2, is ∼1033 ergs.s–1. Although these two X-ray sources are attributable to young stellar objects (YSOs) in the same H II complex, they are in sharp contrast; the one at the center of the H II complex exhibits strong K-shell transition lines of iron, while the other near the east has only weak lines. The other H II complexes, Sgr B2 North and South, also show hard and highly absorbed X-ray emissions due possibly to the star formation activity. The composite X-ray spectrum of the other cloud member X-ray sources is fitted with a thin thermal plasma of ∼10 keV temperature with hydrogen column density (NH) of 1.3x1023Hcm–2 and individual X-ray luminosity of a few times 1031-1032 ergs.s–1. These are likely to be a single YSO or cluster of YSOs, but neither radio nor infrared counterpart is found. An alternative scenario of isolated white dwarfs powered by Bondi-Hoyle accretion from the dense cloud gas is also discussed. The X-ray spectra exhibit an additional 6.4 keV line of neutral or low-ionization irons, which indicates that the environment gas is concentrated near the sources.