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arXiv 1202.0489astro-ph.HE
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用XMM-牛顿观测到的处于静止状态的神秘黑洞候选者和X射线瞬态IGR J17091-3624

The enigmatic black-hole candidate and X-ray transient IGR J17091-3624 in its quiescent state as seen with XMM-Newton

Rudy Wijnands, Yi Jung Yang, Diego Altamirano

备注：
Submitted to MNRAS letters
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摘要：

我们报告两个短的XMM-牛顿观测在2006年8月和2007年2月期间的神秘的黑洞候选人系统IGR J17091-3624的静止状态。在这两次观测中，都清楚地发现了放射源。虽然估计通量的误差很大，但与2006年8月的观测相比，2007年2月的观测似乎亮了几十个单位。在这两次观测中，2-10 keV的源的光度接近~10^{33} erg/s，假设距离为10 kpc。然而，我们注意到，到这个源的距离并没有很好的限制，有人建议它可能远至35千秒差距，这将导致一个数量级的更高的光度。如果经验发现的轨道周期和黑洞瞬变的静止光度之间的关系对于IGR J17091-3624也是有效的，那么我们可以估计在10 kpc的距离上轨道周期大于100小时（大于4天），但是如果源真的更远的话，它可能大到几十天。如此大的轨道周期与GRS 1915+105类似，后者的轨道周期约为34天。如此大的轨道周期可能与两个源都表现出同样非常剧烈和极端快速的X射线变化有关，到目前为止，还没有从任何其他黑洞系统中看到过这种变化。另外，IGR J17091-3624的轨道周期可能与其他系统更一致（<100小时），但我们碰巧观察到该源的吸积速率明显高于其真实的静态吸积速率。在这种情况下，IGR J17091-3624和GRS 1915+105所见的极端短期变化特性的存在或不存在与这些黑洞系统的轨道周期无关。

英文摘要：

We report on two short XMM-Newton observations performed in August 2006 and February 2007 during the quiescence state of the enigmatic black hole candidate system IGR J17091-3624. During both observations the source was clearly detected. Although the errors on the estimated fluxes are large, the source appears to be brighter by several tens of percents during the February 2007 observation compared to the August 2006 observation. During both observations the 2-10 keV luminosity of the source was close to ~10^{33} erg/s for an assumed distance of 10 kpc. However, we note that the distance to this source is not well constrained and it has been suggested it might be as far as 35 kpc which would result in an order of magnitude higher luminosities. If the empirically found relation between the orbital period and the quiescence luminosity of black hole transients is also valid for IGR J17091-3624, then we can estimate an orbital period of >100 hours (>4 days) for a distance of 10 kpc but it could be as large as tens of days if the source is truly much further away. Such a large orbital period would be similar to GRS 1915+105 which has an orbital period of ~34 days. Orbital periods this large could possibly be connected to the fact that both sources exhibit the same very violent and extreme rapid X-ray variability which has so far not yet been seen from any other black hole system. Alternatively the orbital period of IGR J17091-3624 might be more in line with the other systems (<100 hours) but we happened to have observed the source in an episode of elevated accretion which was significantly higher than its true quiescent accretion rate. In that case, the absence or presence of extreme short-term variability properties as is seen for IGR J17091-3624 and GRS 1915+105 is not related to the orbital periods of these black hole systems.

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