Broad-band X-ray observations of the Orion region with ASCA

Broad-band X-ray images and spectra of the Orion Nebula region were obtained with the X-ray satellite ASCA. Fifty two point-like sources were resolved, including the Orion Trapezium. A large fraction of the optical counterparts of the ASCA sources were classified as G-M type stars. Spectral model fits and count ratios (flux ratio between soft and broad bands) revealed that most of the point sources exhibit a high-temperature plasma of similar to 2-5 keV. Model fits of the X-ray spectra from extended regions around the Orion Nebula (M42), the reflection nebula NGC 1977, and the sky between these nebulae required at least two-temperature components of typically 0.7-1 keV and 3-5 keV. From selected high-flux sources, we also found that the model of a 2-temperature thin thermal plasma is more likely than that of a single-temperature. X-ray light curves from these sources were time variable, but showed no large flares. We thus suggest that the hard X-rays are generated even in relatively quiescent states.