Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...545..290a&link_type=abstract
The Astrophysical Journal, Volume 545, Issue 1, pp. 290-300.
Astronomy and Astrophysics
Astronomy
25
Galaxy: Structure, Ism: Clouds, Ism: Structure, X-Rays: Ism
Scientific paper
Observations of the diffuse X-ray background at energies ~3/4 and 1.5 keV show a large region of enhanced emission around the Galactic center. The origin of this X-ray enhancement is not known, but the best candidates are the nearby Loop I superbubble and a Galactic X-ray bulge. To differentiate between these two possibilities, the distance scales to the X-ray-emitting material along the line of sight must be established. A mosaic of 13 ROSAT PSPC pointings in the direction of l~337deg, b~4deg reveals X-ray shadows in the 3/4 and 1.5 keV bands cast by a distant molecular cloud complex. Analysis of the shadows indicates that a large fraction (45%+/-9%) of the observed emission in this direction originates beyond the cloud complex, located at d~2 kpc. The implied surface brightness of this distant emission source can account for ~70% of the enhanced emission away from the absorption trough in the Galactic plane. This result indicates that the Loop I bubble cannot be the principal source of the enhanced X-ray emission, and suggests the existence of a bright X-ray source occupying the central region of the Galaxy, with a radial extent of ~6 kpc and an X-ray luminosity of ~1039 ergs s-1. We examine some simple models of the emission region and compare them to the ROSAT all-sky survey. A thermal origin for the emission implies a plasma temperature of ~4×106 K and a total thermal energy in the range of 6-9×1055 ergs.
Almy R. C.
Bronfman Leonard
Digel Seth William
May Jorge
McCammon Dan
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