SIMBAD references

We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-Ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the submillimeter-millimeter dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3)x10²³ H.cm^–2. Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be ∼10³⁰ ergs.s^–1 at a distance of 450 pc. From the large absorption, positional coincidence, and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores.We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3x10²³ H.cm^–2 indicates that the source must be surrounded by dense gas, suggesting that it is either a young stellar object in an early accretion phase or a Type II AGN (e.g., a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T Tauri phase.