Session 18 - The Interstellar Medium.
Oral session, Monday, June 08

## [18.03] The Structure of the Soft X-ray Background in the Galactic Plane

S. Park (Purdue University)

With mosaics of the ROSAT PSPC pointed observations, the structure of the 0.1 - 2.0 keV soft X-ray background in the Galactic plane (0^\circ < l < 26^\circ) is studied. In the 0.25 keV band, degree scale X-ray intensity variations are detected at \pm10% level about the mean. This intensity variation implies a contribution from a relatively thin emission region such as a clumpy boundary shell of the Local Hot Bubble to the observed 0.25 keV flux. In the 0.75 and 1.5 keV band, several shadows in the diffuse X-ray background cast by molecular clouds are detected. These shadows indicate that 15% - 60% of the observed diffuse X-ray emission originates from behind 0.1 - 3 kpc from the Sun. These deep shadows imply a highly enhanced X-ray emitting region around the Galactic center: existence of a Galactic X-ray bulge.