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The rms-flux relation of Cyg X-2 in the horizontal branch

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Abstract

We have investigated the relation between the root mean square (rms) variability and the X-ray flux (rms-flux relation) of the Z source Cyg X-2, and as well the energy dependence based on the Rossi X-ray Timing Explorer (RXTE) observations. We currently focus on the horizontal branch (HB), due to the negative correlation in flux of the soft and the hard X-rays. The rms-flux correlation has energy dependence as follows: positive at hard X-rays (above 10 keV) but negative at soft X-rays (below 10 keV). This provides a feature different from the previous one, and may be suggestive of different origins of X-rays below and above 10 keV. Nevertheless, the overall spectrum can be well fitted with a model consisting of a blackbody and Comptonization components, but the fitting results do not reveal any features around 10 keV that could account for such a change in the rms-flux relation.

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Authors and Affiliations

  1. Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing, 100049, China

    ZhiBing Li, YaJuan Lei, JinLu Qu, Shu Zhang & LiMing Song

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  1. ZhiBing Li
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  2. YaJuan Lei
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  3. JinLu Qu
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  4. Shu Zhang
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  5. LiMing Song
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Correspondence to ZhiBing Li.

Additional information

This work was supported by the National Basic Research Program of China (Grant No. 2009CB 824800), the CAS Key Project (Grant No. KJCX2-YW-T03), the National Natural Science Foundation of China (Grant No. 10773017), and the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (Grant No. 200821164).

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Li, Z., Lei, Y., Qu, J. et al. The rms-flux relation of Cyg X-2 in the horizontal branch. Sci. China Phys. Mech. Astron. 53 (Suppl 1), 86–90 (2010). https://doi.org/10.1007/s11433-010-0007-3

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  • DOI: https://doi.org/10.1007/s11433-010-0007-3

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