Shu-Ping Yan, Guo-Qiang Ding, Na Wang, Jin-Lu Qu, Li-Ming Song
A statistical study is made on both the energy dependence of the low-frequency QPO amplitude (LFQPO amplitude spectrum) and the LFQPO amplitude from all the {\it RXTE} observations of GRS 1915+105. Based on the two-branch correlation of the LFQPO frequency and the hardness ratio, the observations which are suitable for evaluating the LFQPO amplitude spectrum are divided into two groups. According to a comparison between the radio and X-ray emissions, we deduce that the jets during the two group observations are very different. A negative correlation between the LFQPO frequency and the radio flux is found for one group. The LFQPO amplitude spectrum is fitted by a power-law with an exponential cutoff for quantitatively describing. It reveals that as the LFQPO frequency increases, the power-law hardens. And the cutoff energy firstly decreases, and then smoothly levels off. The fit also shows that the LFQPO amplitude spectra of the two groups are essentially the same, suggesting that the LFQPO seems not to originate from the jet. The LFQPO amplitude spectra are hard, indicating a possible origin of the LFQPO in the corona. As the LFQPO frequency increases, the LFQPO amplitude firstly increases and then decreases. The impacts of the low pass filter and the jet on the LFQPO amplitude are discussed.
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http://arxiv.org/abs/1306.0640
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