A Measurement of the Broadband Spectrum of XTE J1118+480 with BeppoSAX and Its Astrophysical Implications
A Measurement of the Broadband Spectrum of XTE J1118+480 with BeppoSAX and Its Astrophysical Implications
复制标题
DOI：
10.1086/323258
复制
发表时间：
2001-07
期刊：
影响因子：
--
通讯作者：
F. Frontera;A. Zdziarski;L. Amati;J. Mikołajewska;T. Belloni;S. del Sordo;F. Haardt;E. Kuulkers;N. Masetti;M. Orlandini;E. Palazzi;A. Parmar;R. Remillard;A. Santangelo;L. Stella
中科院分区：
文献类型：
--
作者：
F. Frontera;A. Zdziarski;L. Amati;J. Mikołajewska;T. Belloni;S. del Sordo;F. Haardt;E. Kuulkers;N. Masetti;M. Orlandini;E. Palazzi;A. Parmar;R. Remillard;A. Santangelo;L. Stella
我们报告了 2000 年 4 月 14 日至 15 日使用 BeppoSAX 卫星的窄场仪器（0.1-200 keV）对 X 射线瞬变 XTE J1118+480 进行的机会目标观测的结果。测量的光谱符合幂律，光子指数约为 1.7，并通过超软 X 射线过量和高于约 100 keV 的高能截止进行了修改。软过剩与温度约为 40 eV 和低通量的黑体一致，而截止幂律与电子温度约为 102 keV 且光学深度为 1 的等离子体中的热康普顿化非常吻合。与黑体的弱点一致，康普顿反射也很弱。尽管数据与吸积气体的热相和冷相的各种几何形状一致，但我们得出结论，热吸积盘是最合理的模型。最近对质量和距离的估计暗示的爱丁顿比率约为 10-3，这可能表明平流可能不是主要的冷却机制。最后，我们认为反射介质具有较低的金属丰度，这与系统在光环中的位置一致。
We report on results of a Target-of-Opportunity observation of the X-ray transient XTE J1118+480 performed on 2000 April 14-15 with the Narrow Field Instruments (0.1-200 keV) of the BeppoSAX satellite. The measured spectrum is a power law with a photon index of ~1.7 modified by an ultrasoft X-ray excess and a high-energy cutoff above ~100 keV. The soft excess is consistent with a blackbody with a temperature of ~40 eV and a low flux, while the cutoff power law is well fitted by thermal Comptonization in a plasma with an electron temperature of ~102 keV and an optical depth of order unity. Consistent with the weakness of the blackbody, Compton reflection is weak. Although the data are consistent with various geometries of the hot and cold phases of the accreting gas, we conclude that a hot accretion disk is the most plausible model. The Eddington ratio implied by recent estimates of the mass and the distance is ~10-3, which may indicate that advection is probably not the dominant cooling mechanism. We finally suggest that the reflecting medium has a low metallicity, consistent with the location of the system in the halo.