Discovery of Hard X-Rays from a Cluster of Protostars

We report on the detection of hard X-rays from protostar candidates (Class I sources) in the R Coronae Australis (R CrA) molecular cloud. The hard X-rays are found even in the quiescent states with extremely high temperature of about 6 keV. One of the sources, probably the embedded far-infrared source R1, exhibited a powerful X-ray flare. These phenomena are similar to, but with a significantly higher temperature than, those seen in T Tauri stars. The flare spectrum is unusual, showing a broadened or double emission-line structure between 6.2 and 6.8 keV. Since X-rays are unexpected from current protostellar theory, these ASCA observations should have a significant impact on our understanding of star formation and the earliest phases of stellar evolution.