[论文解读] Unveiling the nature of INTEGRAL objects through optical spectroscopy. IX. 22 more identifications, and a glance into the far hard X-ray Universe

N. Masetti, P. Parisi+15 more|arXiv (Cornell University)|Jan 9, 2012

Astrophysics and Cosmic Phenomena参考文献 83被引用 25

一句话总结

本研究通过六台望远镜的光学光谱观测，识别出22个此前未知或研究不足的硬X射线源，这些源由INTEGRAL卫星探测到。研究确认了16个活动星系核（AGNs），包括一个红移z = 3.12的源——这是迄今第二遥远的INTEGRAL源——以及六个银河系天体，表明AGNs主导了硬X射线源的分布，并凸显了深度INTEGRAL巡天在探测高红移和遮蔽AGNs中的作用。

ABSTRACT

(Abridged) Since its launch in October 2002, the INTEGRAL satellite has revolutionized our knowledge of the hard X-ray sky thanks to its unprecedented imaging capabilities and source detection positional accuracy above 20 keV. Nevertheless, many of the newly-detected sources in the INTEGRAL sky surveys are of unknown nature. The combined use of available information at longer wavelengths (mainly soft X-rays and radio) and of optical spectroscopy on the putative counterparts of these new hard X-ray objects allows us to pinpoint their exact nature. Continuing our long-standing program that has been running since 2004, and using 6 different telescopes of various sizes, we report the classification through optical spectroscopy of 22 more unidentified or poorly studied high-energy sources detected with the IBIS instrument onboard INTEGRAL. We found that 16 of them are active galactic nuclei (AGNs), while the remaining 6 objects are within our Galaxy. Among the identified extragalactic sources, 14 are Type 1 AGNs; of these, 6 lie at redshift larger than 0.5 and one has z = 3.12, which makes it the second farthest object detected in the INTEGRAL surveys up to now. The remaining AGNs are of type 2, and one of them is a pair of interacting Seyfert 2 galaxies. The Galactic objects are identified as two cataclysmic variables, one high-mass X-ray binary, one symbiotic binary and two chromospherically active stars. We thus still find that AGNs are the most abundant population among hard X-ray objects identified through optical spectroscopy. Moreover, we note that the higher sensitivity of the more recent INTEGRAL surveys is now enabling the detection of high-redshift AGNs, thus allowing the exploration of the most distant hard X-ray emitting sources and possibly of the most extreme blazars.

研究动机与目标

• 识别INTEGRAL IBIS仪器探测到的22个此前未分类或研究不足的硬X射线源的真实性质。
• 利用多波段数据和光学光谱，确定这些高能源的物理特性。
• 评估高红移和遮蔽AGNs对硬X射线背景的贡献。
• 通过结合软X射线定位与光学后续观测，提高源关联的准确性。
• 评估光谱后续观测在解析未识别INTEGRAL源性质方面的有效性。

提出的方法

• 利用分布在多个大洲的六台地面望远镜，对22个INTEGRAL硬X射线源的候选对应体进行了光学光谱观测。
• 光谱分类基于发射线特征，区分I型（宽线）和II型（窄线）AGNs。
• 将软X射线（Chandra、XMM-Newton、Swift）、射电、红外和光学巡天的多波段数据进行交叉比对，以优化源关联。
• 通过发射线红移测量确定红移，其中IGR J12319−0749源被确认为z = 3.12。
• 利用最新的INTEGRAL全天巡天数据（第4版IBIS星表和7年巡天数据）对源群体进行统计分析。
• 本研究建立在2004年起启动的长期光谱后续观测计划基础上，整合了204个已识别源的数据。

实验结果

研究问题

• RQ1 INTEGRAL在20–100 keV能段探测到的22个此前未识别的硬X射线源的真实本质是什么？
• RQ2 其中有多少是高红移AGNs？它们的分布揭示了硬X射线宇宙的哪些信息？
• RQ3 银河系天体在INTEGRAL巡天中对硬X射线源群体的贡献程度如何？
• RQ4 当缺乏软X射线定位时，光学光谱能否有效解决源关联的模糊性？
• RQ5 通过此方法识别出的遮蔽或光学厚AGNs占硬X射线背景的多大比例？

主要发现

• 22个已识别源中的16个是活动星系核（AGNs），证实AGNs是硬X射线源中占主导地位的群体。
• 16个AGNs中的14个为I型（宽发射线），表明其核心未被遮挡或遮挡程度较弱。
• 一个AGN（IGR J12319−0749）的红移为z = 3.12，使其成为迄今INTEGRAL巡天中第二遥远的源。
• 在六个银河系源中，两个为新星爆发变星，一个为大质量X射线双星，一个为共生双星，两个极可能是RS CVn型活动恒星。
• 本研究证实，光学光谱在源识别方面仍极为有效，自2004年以来该计划获得的204次光谱识别中，85%已成功完成。
• 近期INTEGRAL巡天更高的灵敏度使高红移AGNs的探测成为可能，为研究最遥远且极端的硬X射线发射源打开了新窗口。