标题： 搜索Grossan目录中的变化型活动星系核(AGN) 显示英文标题

标题： A search for changing-look AGN in the Grossan catalog

摘要： 我们使用XMM-Newton观测了来自Grossan星表的4个目标，目的是寻找新的“变脸”活动星系核（AGN）。 样本包括所有在后续观测中表现出比HEAO A-1测量值低得多流量的源：NGC 7674、NGC 4968、IRAS 13218+0552 和 NGC 1667。 在XMM-Newton观测期间，这些源均未处于高流量状态，分析表明它们都可能是康普顿厚的天体。 我们认为，对于所有源，HEAO A-1源识别和流量测量方面可能存在的问题使我们无法确定HEAO A-1的数据是否代表这些源的一个假定的“高”态。 尽管如此，基于GINGA观测的高流量状态和康普顿薄谱线，NGC 7674很可能是已知的第六个“变脸”塞弗特2型星系。 从X射线变化模式来看，我们可以估计这个目标中环状内壁距离的下限约为几秒差距。 值得注意的是，尽管IRAS 13218+0552目前被分类为具有大[OIII]流量的塞弗特1型星系，但XMM-Newton未能探测到它。 然而，原始分类很可能受到发射线中极端速度外流成分的影响。 该天体很可能隐藏着一个高度遮蔽的AGN，并应重新归类为2型源。 显示英文摘要

摘要： We observed with XMM-Newton 4 objects selected from the Grossan catalog, with the aim to search for new 'changing-look' AGN. The sample includes all the sources which showed in subsequent observations a flux much lower than the one measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None of the sources was caught in a high flux state during the XMM-Newton observations, whose analysis reveal they are all likely Compton-thick objects. We suggest that, for all the sources, potential problems with the HEAO A-1 source identification and flux measurement prevent us from being certain that the HEAO A-1 data represent a putative 'high' state for these objects. Nonetheless, based on the high flux state and Compton-thin spectrum of its GINGA observation, NGC 7674 represents probably the sixth known case of a 'changing-look' Seyfert 2 galaxy. From the X-ray variability pattern, we can estimate a likely lower limit of a few parsec to the distance of the inner walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected by XMM-Newton, despite being currently classified as a Seyfert 1 with a large [OIII] flux. However, the original classification was likely to be affected by an extreme velocity outflow component in the emission lines. The object likely harbors an highly obscured AGN and should be re-classified as a Type 2 source.