SS 433的周期性X射线光变研究

Periodicity Analysis of X-ray Light Curves of SS 433

SS 433是目前为止唯一一个被同时检测到轨道周期、超轨道周期和章动周期且存在双向螺旋状喷流的X射线双星系统,通过研究它的X射线光变将有助于理解系统的动力学过程及与其他波段的相关性.利用Lomb-Scargle周期图法(简称LS周期图)和加权小波Z变换法(Weighted Wavelet Z-transform,WWZ)对SS 433的Swift/BAT(Burst Alert Telescope)(15–50 ke V)和RXTE/ASM(Rossi X-Ray Timing Explorer/All-Sky Monitor)(1.5–3,3–5和5–12 ke V)光变曲线进行周期提取,并对得到的周期成分进行蒙特卡洛仿真.其中15–50 ke V能段:检测到5个较强的周期成分P_1(～6.29 d)、P_2(～6.54 d)、P_3(～13.08 d)、P_4(～81.50 d)和P_5(～162.30 d);3–5和5–12 ke V能段:都检测到P_3(～13d)和P_5(～162 d)的周期成分;1.5–3 ke V能段:未检测到任何明显的周期存在.3–5、5–12和15–50 ke V能段的功率谱上最强的周期信号均为P_5,且P_5与之前对光学光变曲线研究得到的结果一致,结合SS 433的螺旋形射电喷流,推测周期为～162 d的X射线和光学波段光变与相对论性喷流的进动有关,X射线与光学光变周期的一致性也表明两个波段的辐射机制有内秉联系.P_3与之前研究中检测到的系统轨道周期(～13.07 d)一致,P_2和P_4则分别为P_3和P_5的一个高频谐波成分.P_1成分仅在15–50 ke V能段的功率谱中被检测到,且它与系统的章动周期一致.随着能段能量的降低(硬X射线到软X射线),所检测到的周期成分却越来越少,这一结果很好地印证了高能段(硬X射线)辐射主要来自于喷流,低能段(软X射线)辐射则可能是由双星系统周围的介质主导.通过分析得到的多个X射线光变周期,为今后SS 433的多波数据分析、系统的动力学机制等研究提供有力的参考依据.

SS 433 is the only X-ray binary to date that was detected to have a pair of well-collimated jets, and its orbital period, super orbital period, and nutation period were all detected at the same time. The study on the periodic X-ray variabilities is helpful for understanding its dynamic process of the central engine and the correlation with other bands. In the present paper, two time series analysis techniques, LombScargle periodogram and weighted wavelet Z-transform, are employed to search for the periodicities from the Swift /BAT（Burst Alert Telescope）（15–50 ke V） and RXTE /ASM（Rossi X-Ray Timing Explorer /All-Sky Monitor）（1.5–3, 3–5 and 5–12 ke V） light curves of SS 433, and the Monte Carlo simulation is performed. For the 15–50 ke V energy band, five significant periodic signals are detected, which are P1（～6.29 d）, P2（～6.54d）, P3（～13.08 d）, P4（～81.50 d）, and P5（～162.30 d）. For the 3–5 and 5–12 ke V energy bands, periodic signals P3（～13 d） and P5（～162 d） are detected in both energy bands.However, for the 1.5–3 ke V energy band, no significant periodic signal is detected. P5 has the strongest periodic signal in the power spectrum for all the energy bands of3–5, 5–12, and 15–50 ke V, and it is consistent with that obtained by previous study in optical band. Further, due to the existence of relativistic radio jets, the X-ray and optical band variability of P5（～162 d） is probably related to the precession of the relativistic jets. High coherence between X-ray and optical light curves may also imply that the X-ray and optical emissions are of the same physical origin. P3 shows a good agreement with the orbital period（～13.07 d） first obtained by previous study, and P2 and P4are the high frequency harmonic components of P3 and P5, respectively. P1 is detected from the power spectrum of 15–50 ke V energy band only, and it is consistent with the systematic nutation period. As the power of energy band decreases（from hard X-ray to soft X-ray）, less periodicities are detected, which provides an evidence that the emission from high energy band（hard X-ray） comes primarily from jets, and the emission from low energy band（soft X-ray） may originate from the medium around binary systems. The multiple X-ray periods obtained from the present studies provide the necessary basis for the analysis of multi-wavelength data and the dynamics of the central engine system of SS 433.