Discovery of Nonthermal X-Ray Emission from the Embedded Massive Star-forming Region RCW 38

We report on results of a 96.7 ks Chandra observation of one of the youngest, most embedded and massive young stellar clusters studied to date in X-rays—RCW 38. We find a region of extended emission about 1.25 × 1.75 pc. The emission is consistent with synchrotron emission. The power index of the emission steepens toward the cluster core, implying that the magnetic field originates there. This is the first evidence of synchrotron emission filling a region of active star formation. The source of the necessary magnetic field is unclear. We measure the hydrogen column to the emission and find that N H increases from 7.6 × 10 21 to 1.61 × 10 22 cm -2 , increasing from the northwest to the southeast quadrants of the cluster, consistent with near-infrared extinction data.