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OMC-3 0类原恒星候选体X射线的发现

Discovery of X rays from Class 0 protostar candidates in OMC-3

Yohko Tsuboi, Katsuji Koyama, Kenji Hamaguchi, Ken'ichi Tatematsu, Yutaro Sekimoto, John Bally, Bo Reipurth

备注：
9 pages, To be appeared in ApJ v554 n2 Jun 20, 2001 issue, related press release is available at http://science.psu.edu/alert/Tsuboi11-2000.htm, Figure 1 and figure 2 with the best resolution is available at ftp.astro.psu.edu/pub/tsuboi/OMC/010205/
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摘要：

我们用钱德拉X射线天文台（CXO）观测了猎户座分子云2和3（OMC-2和OMC-3）。OMC-3的北部被发现特别富含新的X射线特征;四个硬X射线源位于云核的丝状体中。两个源与MMS 2和3的子$mm$ - $mm$尘埃凝聚或外流射电源VLA 1的位置一致，它们处于恒星形成的非常早期阶段。这些源的X射线谱显示出一个（1-3）× 10^23 H cm-2的吸收柱。假设是中等温度的等离子体，在450 pc的距离上，0.5 ~ 10 keV波段的X射线光度估计为~10^30 erg·s^-1。从大的吸收，位置重合和中等亮度，我们推断，硬X射线是来自非常年轻的恒星物体嵌入在分子云的核心。我们在尘埃丝边缘发现了另一个硬X射线源。3 x 10^23 H cm^-2的极高吸收表明，该源必须被致密气体包围，这表明它要么是处于早期吸积阶段的YSO，要么是II型活动星系核（例如塞弗特2），尽管在其他任何波长都没有发现对应的物质。与硬X射线源相反，软X射线源被发现分布在尘埃丝周围，其中大部分被识别为金牛座T阶段的红外源。

英文摘要：

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 sub$mm$-$mm$ 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) x 10^23 H cm-2. Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be ~10^30 erg 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 3 x 10^23 H cm^-2 indicates that the source must be surrounded by dense gas, suggesting that it is either a YSO 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.

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