SMALL - SCALE VARIATIONS IN THE keV X - RAY BACKGROUND ALONG THE 14 GALACTIC PLANE

Forty-two ROSAT Position Sensitive Proportional Counter pointed observations in the Ðrst quadrant (l D 4¡È26¡) of the Galactic plane are mosaicked in order to study the spatial structure of the X-rayÈ emitting gas in the Local Hot Bubble (LHB). X-ray intensity variations at various angular scales are examined in the keV band, and degree-scale variations are detected. In the context of the LHB and the 14 displacement model for the origin of the keV band background, the hardness ratio, angular size, and 14 magnitude of the intensity variations suggest that at the ^10% level there is an inÑuence of a clumpy boundary structure superposed upon the emission from the uniformly distributed D106 K plasma of the LHB interior. The possible origins of such a clumpy boundary structure of the LHB are discussed with Rayleigh-Taylor instabilities and clumping of the cooler interstellar medium at the boundary region being likely candidates. Subject headings : di†use radiation È ISM: bubbles È ISM: structure È X-rays : ISM