為了得到第一部分與第二部分各自的最佳自轉與公轉參數，本論文使用脈衝抵達時間延遲與 Tse et al. (2020) 提出的方法，以疊代的方式求出自轉與公轉參數修正量，藉此得到精確的參數。接著探討時間噪音 (flux-dependent timing noise) 對中子星自轉相位的影響。首先將第一部分、第二部分及整體觀測數據的資料點用各自的最佳自轉與公轉參數擬合後，得到各個資料點的脈衝基準點相位，接著代入與X光強度相關的時間噪音關係式 (Kulkarni, A. K., & Romanova 2013) 進行修正，然而擬合的結果並沒有明顯的改善。在本研究中認為，由於第一部分、第二部分及整體觀測數據分別用了不同組的自轉與公轉參數，而整體觀測數據包含的資料點多、其自轉與公轉參數較為準確，所以凸顯了時間噪音的效應。
再來依照能量將光子區分成 11 個能帶，使用互相關 (cross-correlation) 的方法比較各個能帶能量間的脈衝時間延遲 (energy dependent pulse arrival time delay)。在本研究中，觀察到第一部分與第二部分皆存在低能延遲 (soft lag) 現象。在脈衝強度 (pulsed fraction) 分布方面，脈衝強度在 1-5 keV 的範圍裡逐漸上升，在更高能量的能帶裡逐漸降低。低能延遲與脈衝強度變化的現象，都能用黑體輻射分量較強的二分量模型與吸積盤熱輻射解釋。;IGR J17591-2342, an accreting millisecond X-ray pulsar, was discovered in 2018 with a pulsation frequency of 527 Hz. From Neutron star Interior Composition Explorer observation during its 2018 outburst, two rebrightenings were found. The research goal of this thesis is to investigate the spin and orbital parameters and the energy dependent pulse behaviors for these two rebrightenings (part 1 and part 2).
In order to obtain the spin and orbital parameters for part 1 and part 2, pulse arrival time delay was used. The accurate spin and orbital parameters can be estimate by iterative method proposed by Tse et al. (2020). Next, we discussed the effect of flux-dependent timing noise on the neutron star′s rotation phase. After fitting the data points of part 1, part 2 and the overall observation data with their respective accurate spin and orbital parameters, the pulse phase evolution was obtained. Then we attempted to improve the fitting by applying the flux-depend timing noise model proposed by Kulkarni, A. K., & Romanova (2013). However, the fitting results shows no significant improvement. In this study, it is believed that since part 1, part 2 and the overall observation data used different sets of spin and orbital parameters respectively, and the overall observation data contains the more data points so its spin and orbital parameters are the more accurate, which highlights the effect of timing noise.
The photons were divided into 11 energy bands to compare the energy dependent pulse arrival time delay through cross-correlation method. The soft lag phenomenon is observed in both part 1 and part 2. The pulsed fraction amplitude increases from 1 to 5 keV and then decreases at higher energy band. These phenomena can be explained by the two-component model with a strong blackbody component and the thermal radiation from the accretion disc.
