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...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.展开更多
Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of freq...Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of frequency resolution is limited by data length and observation time. Longer observation time or oversampling can be employed to improve frequency analysis results, but with greatly increased computational complexity and large amounts of sampling data. This greatly restricts real-time autonomous navigation based on X-ray pulsars. To resolve this issue, a new method based on frequency subdivision and the continuous Lomb periodogram （CLP） is proposed to improve precision of period estimation using short-time observation data. In the proposed method, an initial frequency is first calculated using fast Lomb periodogram. Then frequency subdivision is per- formed near the initial frequency to obtain frequencies with higher precision. Finally, a refined period is achieved by calculating the CLP in the obtained frequencies. Real data experiments show that when observation time is shorter than 135 s, the proposed method improves period estimation precision by 1-3 orders of magnitude compared with the fast Lomb periodogram and fast Fourier transform （FFT） methods, with only a slight increase in computational complexity. Furthermore, the proposed method performs better than efsearch （a period estimation method of HEAsoft） with lower computational complexity. The proposed method is suitable for estimating periods of X-ray pulsars and obtaining the rotation period of variable stars and other celestial bodies.展开更多
文摘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.
基金Project supported by the National Basic Research Program(973)of China(No.2014CB340205)the National Natural Science Foundation of China(Nos.61301173 and 61473228)the Aerospaced TT&C Innovation Program of 704 Research Institute of China(No.201405B)
文摘Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of frequency resolution is limited by data length and observation time. Longer observation time or oversampling can be employed to improve frequency analysis results, but with greatly increased computational complexity and large amounts of sampling data. This greatly restricts real-time autonomous navigation based on X-ray pulsars. To resolve this issue, a new method based on frequency subdivision and the continuous Lomb periodogram （CLP） is proposed to improve precision of period estimation using short-time observation data. In the proposed method, an initial frequency is first calculated using fast Lomb periodogram. Then frequency subdivision is per- formed near the initial frequency to obtain frequencies with higher precision. Finally, a refined period is achieved by calculating the CLP in the obtained frequencies. Real data experiments show that when observation time is shorter than 135 s, the proposed method improves period estimation precision by 1-3 orders of magnitude compared with the fast Lomb periodogram and fast Fourier transform （FFT） methods, with only a slight increase in computational complexity. Furthermore, the proposed method performs better than efsearch （a period estimation method of HEAsoft） with lower computational complexity. The proposed method is suitable for estimating periods of X-ray pulsars and obtaining the rotation period of variable stars and other celestial bodies.
