X-rays from HH 154

Protostellar jets are observed during all stages of early stellar evolution. X-rays originating within these outflows have been observed only from ten such objects and require shock velocities of about 500 km s(-1). L1551 IRS 5, the driving source of the Herbig-Haro object 154, is heavily absorbed. Therefore, one can study the outflow close to the launching zone without contaminating light from the power source. We present a new third epoch Chandra observation of HH 154 which shows that the majority of the X-ray emission is concentrated within a small region close to the driving source over a timespan of 8 years. Reheating or replenishment of the plasma is required in order to explain the observations. The evolution of the temperature of the X-ray emitting plasma suggests that the heating occurs within the innermost region (similar to 150 AU) of the outflow.