A Statistical Study on the Low-Frequency QPO Amplitude Spectrum and Amplitude in GRS 1915+105

摘要

A statistical study was made on both the energy dependence of thelow-frequency quasi-periodic oscillation (QPO) amplitude (LFQPO amplitudespectrum) and the LFQPO amplitude from all the RXTE observations of GRS1915+105. Based on the two-branch correlation of the LFQPO frequency and thehardness ratio, the observations that were suitable for evaluating the LFQPOamplitude spectrum were divided into two groups. According to a comparisonbetween the radio and X-ray emissions, we deduced that the jets during the twogroups of observations are very different. A negative correlation between theLFQPO frequency and the radio flux was found for one group. The LFQPO amplitudespectrum was fitted by a power-law with an exponential cutoff in order todescribe it quantitatively. It reveals that as the LFQPO frequency increases,the power-law hardens. And the cutoff energy firstly decreases, and thensmoothly levels off. The fit also shows that the LFQPO amplitude spectra of thetwo groups are essentially the same, suggesting that the LFQPO seems not tooriginate from the jet. The LFQPO amplitude spectra are hard, indicating apossible origin of the LFQPO in the corona. As the LFQPO frequency increases,the LFQPO amplitude firstly increases and then decreases. The effects of thelow pass filter and the jet on the LFQPO amplitude are discussed.