X-Rays from Superbubbles in the Large Magellanic Cloud. III. X-Ray--dim Superbubbles

Only X-ray-bright superbubbles have been reported in the past. ROSA T provides an excellent opportunity to study X-ray-dim superbubbles We have analyzed the ROSAT Position Sensitive Proportional Counter observations of four superbubbles in the Large Magellanic Cloud DEM 31, DEM 105, DEM 106, and DEM 137. None of the four is detected at more than the 2 σ level. The observed luminosities and the 3 σ upper limits are consistent with the luminosities expected from energy-conserving bubbles. These results confirm that not all superbubbles are X-ray bright, suggesting that an intermittent process such as hidden supernova remnants is responsible for the X-ray-bright super bubbles.