arXiv 0801.00172008-01astro-ph

激发态OH脉泽和超新星遗迹

Excited-state OH Masers and Supernova Remnants

Ylva M. Pihlström, Vincent L. Fish, Loránt O. Sjouwerman, Laura K. Zschaechner, Philip B. Lockett, Moshe Elitzur

备注：: Accepted to ApJ, 7 pages including 1 table and 4 figures
DOI：: 10.1086/529009

摘要：

碰撞泵浦，基态1720 MHz的氢脉泽线被广泛认为是一个冲击区的示踪剂，并在恒星形成区和超新星遗迹观察。虽然在恒星形成区已经探测到并研究了OH的某些激发态谱线，但超新星遗迹中的OH激发态问题-预计那里的碰撞率很高-只是最近才得到处理。OH的碰撞激发模型表明，1720，4765和6049 MHz脉泽可以发生在类似的条件下，在地区的冲击气体。特别是，6049和4765兆赫脉泽变得更加显着的OH柱密度增加，1720兆赫脉泽开始被淬灭。在超新星遗迹中，激发态OH线脉泽发射的检测，因此可以作为一个探针的区域较高的柱密度。使用甚大阵，我们寻找激发态OH在4.7，7.8，8.2和23.8 GHz的线在四个研究良好的超新星遗迹与强1720 MHz脉泽发射（SgrAEast，W28，W 44和IC 443）。在约10 mJy/光束的典型检测限下，未进行检测。由于VLA接收器没有覆盖这些频率，因此使用Effelsberg进行了6 GHz线路的搜索，并在随附的信件中进行了报告（Fish，Sjouwerman和Pihlstrom 2007）。我们还交叉相关的位置，已知的超新星遗迹的位置，1612兆赫脉泽发射从盲调查。没有发现可能的关联，也许除了在SgrAEast地区。激发态OH的检测的缺乏表明，OH柱密度足以为1720 MHz的反转，但不为激发态跃迁的反转，与C型冲击的预期结果一致。

英文摘要：

The collisionally pumped, ground-state 1720 MHz maser line of OH is widely recognized as a tracer for shocked regions and observed in star forming regions and supernova remnants. Whereas some lines of excited states of OH have been detected and studied in star forming regions, the subject of excited-state OH in supernova remnants -- where high collision rates are to be expected -- is only recently being addressed. Modeling of collisional excitation of OH demonstrates that 1720, 4765 and 6049 MHz masers can occur under similar conditions in regions of shocked gas. In particular, the 6049 and 4765 MHz masers become more significant at increased OH column densities where the 1720 MHz masers begin to be quenched. In supernova remnants, the detection of excited-state OH line maser emission could therefore serve as a probe of regions of higher column densities. Using the Very Large Array, we searched for excited-state OH in the 4.7, 7.8, 8.2 and 23.8 GHz lines in four well studied supernova remnants with strong 1720 MHz maser emission (SgrAEast, W28, W44 and IC443). No detections were made, at typical detection limits of around 10 mJy/beam. The search for the 6 GHz lines were done using Effelsberg since the VLA receivers did not cover those frequencies, and are reported on in an accompanying letter (Fish, Sjouwerman & Pihlstrom 2007). We also cross-correlated the positions of known supernova remnants with the positions of 1612 MHz maser emission obtained from blind surveys. No probable associations were found, perhaps except in the SgrAEast region. The lack of detections of excited-state OH indicates that the OH column densities suffice for 1720 MHz inversion but not for inversion of excited-state transitions, consistent with the expected results for C-type shocks.

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