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arXiv 1502.07669astro-ph.HE
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4U 1705-44的Suzaku宽带谱:探测硬态的反射分量

Suzaku broad-band spectrum of 4U 1705-44: Probing the Reflection component in the hard state

T. Di Salvo, R. Iaria, M. Matranga, L. Burderi, A. D'Ai, E. Egron, A. Papitto, A. Riggio, N. R. Robba, Y. Ueda

摘要:

6.4-6.97 keV的铁发射线(通过K α辐射跃迁识别)是X射线带中最强的离散特征之一。这是推断致密物体周围吸积盘最内部等离子体性质的最强大探测器之一。在本文中,我们提出了一个最近的朱雀观测,100-ks的有效曝光,环礁源和X射线爆发4U 1705-44,在那里我们清楚地检测到的反射分量的签名,这是扭曲的高速运动的吸积盘。反射分量由大约6.4 keV的宽铁线和大约20 keV的高X射线能量的康普顿凸起组成。所有这些功能始终符合反射模型,我们发现,在硬状态的涂抹参数是非常相似的,发现在以前的XMM-牛顿观察在软状态。特别地,我们发现内部盘半径为Rin = 17 +/- 5 Rg(其中Rg是引力半径,GM/c^2),辐射率与圆盘半径的相关性为-2.5 +/- 0.5,相对于视线的倾角为i = 43 +/- 5度,并且盘中的发射区域的外半径为Rout > 200 Rg。我们注意到,吸积盘在大半径处似乎没有被截断,尽管对于中子星,源在爱丁顿光度的3%处处于硬态。我们还发现在低能量,在3.03 +/- 0.03千电子伏,与轻度电离氩(Ar XVI-XVII)发射兼容的宽发射线的证据。氩转换不包括在我们使用的自洽反射模型中,因此我们在模型中添加了一个额外的组件来适应此功能。低能量线似乎与被相同的内部磁盘参数发现的反射分量的涂抹兼容。

英文摘要:

Iron emission lines at 6.4-6.97 keV, identified with Kalpha radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disk around a compact object. In this paper we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disk. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disk radius is Rin = 17 +/- 5 Rg (where Rg is the Gravitational radius, GM/c^2), the emissivity dependence from the disk radius is -2.5 +/- 0.5, the inclination angle with respect to the line of sight is i = 43 +/- 5 degrees, and the outer radius of the emitting region in the disk is Rout > 200 Rg. We note that the accretion disk does not appear to be truncated at large radii, although the source is in a hard state at about 3 % of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 +/- 0.03 keV, compatible with emission from mildly ionized Argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low energy line appears compatible with being smeared by the same inner disk parameters found for the reflection component.

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