Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52

被引:101
作者
Mendez, M
van der Klis, M
van Paradijs, J
Lewin, WHG
Vaughan, BA
Kuulkers, E
Zhang, W
Lamb, FK
Psaltis, D
机构
[1] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[2] Ctr High Energy Astrophys, NL-1098 SJ Amsterdam, Netherlands
[3] Univ Nacl La Plata, Fac Ciencias Astron & Geofis, RA-1900 La Plata, Buenos Aires, Argentina
[4] Univ Alabama, Dept Phys, Huntsville, AL 35899 USA
[5] MIT, Space Res Ctr, Cambridge, MA 02139 USA
[6] CALTECH, Space Radiat Lab, Pasadena, CA 91125 USA
[7] Univ Oxford, Nucl & Astrophys Lab, Oxford OX1 3RH, England
[8] NASA, Goddard Space Flight Ctr, High Energy Astrophys Lab, Greenbelt, MD 20771 USA
[9] Univ Illinois, Dept Phys, Urbana, IL 61801 USA
[10] Univ Illinois, Dept Astron, Urbana, IL 61801 USA
[11] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
基金
美国国家航空航天局;
关键词
accretion; accretion disks; stars; neutron; individual; (4U; 1608-52); X-rays;
D O I
10.1086/311162
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Using a new technique to improve the sensitivity to weak quasi-periodic oscillations (QPOs), we discovered a new QPO peak at about 1100 Hz in the March 1996 outburst observations of 4U 1608-52, simultaneous with the similar to 600-900 Hz peak previously reported from these data. The frequency separation between the upper and the lower QPO peaks varied significantly from 232.7 +/- 11.5 Hz on March 3 to 293.1 +/- 6.6 Hz on March 6. This is the first case of a variable kilohertz peak separation in an atoll source. We discuss to what extent this result could be accommodated in beat-frequency models such as proposed for the kilohertz QPOs. We measured the rms fractional amplitude of both QPOs as a function of energy, and we found that the relation is steeper for the lower than for the upper frequency peak. This is the first source where such a difference between the energy spectrum of the two kilohertz QPOs could be measured.
引用
收藏
页码:L65 / L69
页数:5
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