LMC-2 AS THE BLOWOUT OF A HOT SUPERBUBBLE

Based on the data collected with the imaging proportional counter (IPC) aboard the Einstein Observatory, we have discovered a bright extended X-ray emission region which is enclosed by the supershell LMC-2 identified from optical and radio observations. The diffuse X-rays appear to come from hot gas in a corresponding superbubble. The X-ray count rate of the superbubble is approximately 1.4 counts s-1 in the IPC broad band (0.16-3.5 keV), corresponding to a luminosity of approximately 2 x 10(37) ergs s-1 with a gas temperature approximately 5 x 10(6) K. The bright X-ray emission region appears as a ring with a radius of approximately 15' and correlates well with a cold ISM cavity seen in both the H I and IRAS maps, but is much smaller than the region bounded by the optical filaments. We suggest that LMC-2 has been created by the breakout of the superbubble from the dense galactic plane of the Large Cloud. The bright X-ray emission arises near the plane, where the superbubble is energized by stellar winds and supernova explosions. The blown-out superbubble expands rapidly in the low-density region away from the plane on the far side of the galaxy; its boundary is marked by absorption of soft X-rays in the dense H I shell it creates, and rim-brightened optical filaments at the interface between the hot interior and the cold swept-up medium. This observation represents the first clear evidence of such a hot superbubble in an external galaxy. We go on to speculate that the massive ridge of gas at the eastern edge of the LMC in which the bubble has arisen was formed as a result of the interaction of the LMC disk with the gaseous halo of the Milky Way. The high pressure and density characteristic of this interaction region has triggered the massive star formation which is responsible for creating the superbubble LMC-2.