标题： LSI+61303中的长期周期性作为轨道速率和进动速率的拍频 显示英文标题

标题： Long-term periodicity in LSI+61303 as beat frequency between orbital and precessional rate

摘要： 上下文：在二进制系统LSI+61303中，与轨道周期26.4960 +/- 0.0028天相关的射电爆发峰值通量密度显示出1667 +/- 8天的调制。高空间分辨率下的射电辐射呈现出一个进动喷流的结构，其进动周期为27-28天。目的：射电喷流的进动周期与轨道周期有多接近？射电辐射中的任何周期性都应该通过时间分析来揭示。这项工作的目的是确定进动周期的准确值。方法：我们分析了格林班克干涉仪数据库中6.7年的数据，在2.2 GHz和8.3 GHz频率下使用Lomb-Scargle和相位分散最小化（PDM）方法并进行了模拟。结果：周期图显示两个周期性，P1 = 26.49 +/- 0.07 d（\nu 1=0.03775 d^{-1}）和P2 = 26.92 +/- 0.07 d（\nu 2 = 0.03715 d^{-1}）。 尽管已知射电爆发几乎以轨道周期P1出现，其时间残差表现出令人困惑的锯齿形模式，但本文探讨表明它们实际上是周期性爆发，其周期为Paverage= (2/(\nu 1 + \nu 2)= 26.70 +/- 0.05 d。平均周期Paverage以及长期调制Pbeat=1/(\nu 1 - \nu 2)=1667 +/- 393 d来自于两个接近周期的拍频，即轨道周期P1和进动周期P2。 结论：由天体测量指示的进动周期为27--28 d，即P2=26.92 d。系统\lsi 看起来是天文学中拍频的又一个例子，即当两个物理过程产生几乎相等频率的稳定变化时出现的现象。 频率的微小差异导致了周期为1/(\nu 1-\nu 2)的长期变化。 1667 d的长期调制来自于两个接近的轨道和进动速率的拍频。 显示英文摘要

摘要： Context: In the binary system LSI+61303 the peak flux density of the radio outburst, which is related to the orbital period of 26.4960 +/- 0.0028d, exibits a modulation of 1667 +/- 8 d. The radio emission at high spatial resolution appears structured in a precessing jet with a precessional period of 27-28 d. Aims: How close is the precessional period of the radio jet to the orbital period? Any periodicity in the radio emission should be revealed by timing analysis. The aim of this work is to establish the accurate value of the precessional period. Methods: We analyzed 6.7 years of the Green Bank Interferometer database at 2.2 GHz and 8.3 GHz with the Lomb-Scargle and phase dispersion minimization (PDM) methods and performed simulations. Results: The periodograms show two periodicities, P1 = 26.49 +/- 0.07 d (\nu1=0.03775 d^{-1}) and P2 = 26.92 +/- 0.07 d (\nu2 = 0.03715 d^{-1}). Whereas radio outbursts have been known to have nearly orbital occurrence P1 with timing residuals exhibiting a puzzling sawtooth pattern, we probe in this paper that they are actually periodical outbursts and that their period is Paverage= (2/(\nu1 + \nu2)= 26.70 +/- 0.05 d. The period Paverage as well as the long-term modulation Pbeat=1/(\nu1 - \nu2)=1667 +/- 393 d result from the beat of the two close periods, the orbital P1 and the precessional P2 periods. Conclusions: The precessional period, indicated by the astrometry to be of 27--28 d, is P2=26.92 d. The system \lsi seems to be one more case in astronomy of beat, i.e., a phenomenon occurring when two physical processes create stable variations of nearly equal frequencies. The very small difference in frequency creates a long-term variation of period 1/(\nu1-\nu2). The long-term modulation of 1667 d results from the beat of the two close orbital and precessional rates.