Phase lag and coherence function of X-ray emission from black hole candidate XTE J1550-564

被引:37
作者
Cui, W [1 ]
Zhang, SN
Chen, W
机构
[1] MIT, Ctr Space Res, Cambridge, MA 02139 USA
[2] Univ Alabama, Dept Phys, Huntsville, AL 35899 USA
[3] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[4] Univ Maryland, Dept Astron, College Pk, MD 20742 USA
基金
美国国家航空航天局;
关键词
black hole physics; stars : individual (XTE J1550-564); stars : oscillations; X-rays : stars;
D O I
10.1086/312520
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report the results from measuring the phase lag and coherence function of X-ray emission from black hole candidate XTE J1550-564. These temporal X-ray properties have been recognized to be increasingly important in providing important diagnostics of the dynamics of accretion flows around black holes. For XTE J1550-564, we found significant hard lag-the X-ray variability in high-energy bands lags behind that in low-energy bands-associated both with broadband variability and quasi-periodic oscillation (QPO). However, the situation is more complicated for the QPO: while hard lag was measured for the first harmonic of the signal, the fundamental component showed significant soft lag. Such behavior is remarkably similar to what was observed of microquasar GRS 1915+105. The phase lag evolved during the initial rising phase of the 1998 outburst. The magnitude of both the soft and hard lags of the QPO increases with X-ray flux., while the Fourier spectrum of the broadband lag varies significantly in shape. The coherence function is relatively high and roughly constant at low frequencies and begins to drop almost right after the first harmonic of the QPO. It is near unity at the beginning and decreases rapidly during the rising phase. Also observed is that the more widely separated the two energy bands are, the less the coherence function between the two. It is interesting that the coherence function increases significantly at the frequencies of the QPO and its harmonics. We discuss the implications of the results on the models proposed for black hole candidates.
引用
收藏
页码:L45 / L48
页数:4
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