J. Wang, H. -K. Chang, C. -Y. Liu
We report the energy dependence of normal branch oscillations (NBOs) in Scorpius X-1, a low-mass X-ray binary (LMXB) Z-source. Three characteristic quantities (centroid frequency, quality factor and fractional root-mean-squared (rms) amplitude) of a QPO signal as functions of photon energy are investigated. We found that the NBO centroid frequency decreases with increasing photon energy when it is below 6-8 keV and turns positively correlated with photon energy at the higher-energy side. The rms amplitude increases significantly with the photon energy below 13 keV, and then flats out in the energy band of 13-20 keV. There is no clear dependence on photon energy for the quality factor. Based on these results, we suggest that the NBO originates mainly from the transition layer.
View original:
http://arxiv.org/abs/1207.3407
No comments:
Post a Comment