Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field
Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field
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DOI：
10.1051/0004-6361:20077765
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发表时间：
2008-01
影响因子：
6.5
通讯作者：
H. C. F. Aharonian;E. al.
中科院分区：
文献类型：
--
作者：
H. C. F. Aharonian;E. al.
我们用H.E.S.Cherenkov望远镜在极高能伽马射线能量(E>；0.1TeV)下观测了W28场(持续~40h)。还对白鹭E>；100 MeV数据进行了重新分析。NANTEN 4米望远镜、银河平面观测和其他CO观测的结果已被用于研究分子云。我们在银盘中发现了与W28东北边界重合的VHE伽马射线发射(HESSJ1801-233)，并在W28以南0.5°处发现了一个源复合体(HESSJ1800-240A、B和C)。VHE微分光子谱符合指数为2.3~2.7的纯指数规律。NANTEN^{12}CO(J=1-0)数据揭示了与VHe发射有关的分子云的位置，以当地的静止速度标准，跨越了约15公里的S^{-1}范围。VHE/分子云组合可能表明HESSJ1801-233和HESSJ1800-240的强子起源，投影中的几个云成分可能对VHE发射有贡献。这些云团的组成覆盖了宽广的速度范围，包括W28(~2kpc)的距离估计，并延伸到~4kpc。假设是强子起源，云成分的距离为2kpc和4kpc，所需的宇宙线密度增强因子(相对于太阳值)在~10到~30的范围内。如果位于2kpc的距离，这样的宇宙线密度可能由像W28这样的信噪比提供。另外和/或另选地，粒子加速可以来自几个已编目的SNR和SNR候选者、能量超紧凑的HII区W28A2、以及HII区M8和M20以及它们相关的疏散星团。建议进行进一步的亚毫米观测，以详细探测10公里S的分子云的动力学，以及它们与W28的可能联系。
We observed the W28 field (for ~40 h) at Very High Energy (VHE) gamma-ray energies (E>0.1 TeV) with the H.E.S.S. Cherenkov telescopes. A reanalysis of EGRET E>100 MeV data was also undertaken. Results from the NANTEN 4m telescope Galactic plane survey and other CO observations have been used to study molecular clouds. We have discovered VHE gamma-ray emission (HESSJ1801-233) coincident with the northeastern boundary of W28, and a complex of sources (HESSJ1800-240A, B and C) ~0.5 deg south of W28, in the Galactic disc. The VHE differential photon spectra are well fit by pure power laws with indices Gamma~2.3 to 2.7. The NANTEN ^{12}CO(J=1-0) data reveal molecular clouds positionally associating with the VHE emission, spanning a ~15 km s^{-1} range in local standard of rest velocity. The VHE/molecular cloud association could indicate a hadronic origin for HESSJ1801-233 and HESSJ1800-240, and several cloud components in projection may contribute to the VHE emission. The clouds have components covering a broad velocity range encompassing the distance estimates for W28 (~2 kpc), and extending up to ~4 kpc. Assuming a hadronic origin, and distances of 2 and 4 kpc for cloud components, the required cosmic ray density enhancement factors (with respect to the solar value) are in the range ~10 to ~30. If situated at 2 kpc distance, such cosmic ray densities may be supplied by a SNR like W28. Additionally and/or alternatively, particle acceleration may come from several catalogued SNRs and SNR candidates, the energetic ultra compact HII region W28A2, and the HII regions M8 and M20 along with their associated open clusters. Further sub-mm observations would be recommended to probe in detail the dynamics of the molecular clouds at velocites >10 km s^{-1}, and their possible connection to W28.