TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. IV. RELATIVISTICALLY BROADENED IRON LINES
TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. IV. RELATIVISTICALLY BROADENED IRON LINES
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DOI：
10.1088/0004-637x/773/1/57
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发表时间：
2012-02
期刊：
影响因子：
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通讯作者：
T. Johannsen;D. Psaltis
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文献类型：
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作者：
T. Johannsen;D. Psaltis
根据无毛定理，天体物理学黑洞完全由它们的质量和自旋来表征，并由克尔度规来描述。这个定理可以通过测量（至少）黑洞时空的三个不同的多极矩来进行观测检验。在本文中，我们在一个框架内计算了候选黑洞周围吸积流发出的荧光铁谱线的轮廓，该框架允许我们将计算作为其质量和自旋的函数，以及测量与克尔度规的潜在偏差的自由参数。我们表明，这种偏差导致线轮廓明显改变，并可能在其特征双峰形状中表现出修改的两个峰的通量比。我们还表明，在克尔黑洞的情况下，圆盘倾角可以独立于自旋和偏差参数在低到中等倾角下进行测量。我们估计，在不久的将来，Astro-H和ATHENA+等x射线任务需要达到的精度，才能解决铁线轮廓中克尔度规的偏差，并表明对这种偏差的限制在快速旋转的黑洞中是最强的。更一般地说，我们表明，在圆盘倾角为30°或60°时，以~ 5%的精度测量线轮廓将自旋值的偏差参数限制为一个单位。
According to the no-hair theorem, astrophysical black holes are fully characterized by their masses and spins and are described by the Kerr metric. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we calculate the profiles of fluorescent iron lines emitted from the accretion flows around black hole candidates within a framework that allows us to perform the calculation as a function of its mass and spin as well as of a free parameter that measures potential deviations from the Kerr metric. We show that such deviations lead to line profiles that are significantly altered and may exhibit a modified flux ratio of the two peaks in their characteristic double-peaked shape. We also show that the disk inclination can be measured independently of the spin and the deviation parameter at low to intermediate inclination angles, as in the case of Kerr black holes. We estimate the precision that near-future X-ray missions such as Astro-H and ATHENA+ are required to achieve in order to resolve deviations from the Kerr metric in iron line profiles and show that constraints on such deviations will be strongest for rapidly spinning black holes. More generally, we show that measuring the line profile with a precision of ∼5% at disk inclinations of 30° or 60° constrains the deviation parameter to order unity for values of the spin a ≳ 0.5M.