ROSAT survey diffuse X-ray background maps .2.

This paper presents new maps of the soft X-ray background from the ROSAT all-sky survey. These maps represent a significant improvement over the previous version in that (1) the position resolution of the PSPC has been used to improve the angular resolution from similar to 2 degrees to 12', (2) there are six energy bands that divide each of the previous three into two parts, and (3) the contributions of point sources have been removed to a uniform source flux level over most of the sky. These new maps will be available in electronic format later in 1997. In this paper we also consider the bright emission in the general direction of the Galactic center in the 0.5-2.0 keV band, and the apparent absorption trough that runs through it along the Galactic plane. We find that while the northern hemisphere data are confused by emission from Loop I, the emission seen south of the plane is consistent with a bulge of hot gas surrounding the Galactic center (in our simple model, a cylinder with an exponential fall-off of density with height above the plane). The cylinder has a radial extent of similar to 5.6 kpc. The X-ray emitting gas has a scale height of 1.9 kpc, an in-plane electron density of similar to 0.0035 cm(-3), a temperature of similar to 10(6.6) K, a thermal pressure of similar to 28,000 cm(-3) K, and a total luminosity of similar to 2 x 10(39) ergs s(-1) using a collisional ionization equilibrium (CIE) plasma emission model.