针对精密单点定位时间传递观测模型无法消除二阶电离层延迟误差的实际问题,推导了顾及二阶电离层延迟误差修正的观测模型.应用两个时段实测数据,比较分析了二阶电离层延迟改正前与改正后的精密单点定位测站钟差和时间传递结果.分析表明,二阶电离层延迟对低纬度地区测站钟差影响显著,对中、高纬度的影响逐渐减弱;测站钟差差异序列呈固定偏差加周日变化,固定偏差在南北半球符号相反.二阶电离层对长基线时间传递的影响最大超过26皮秒,对短基线的影响基本可以忽略.据此,提出亚纳秒级长基线时间传递进行二阶电离层延迟修正是必要的,特别是组成基线的测站位于低纬度地区.

基于卫星双向时间传递原理,国家授时中心提出了转发式卫星测定轨方法,已将GEO通信卫星的测定轨精度提高到米级水平.近年来,转发式测定轨技术不断发展完善,观测目标已由单一GEO卫星扩展到北斗IGSO卫星(I1-S).本文描述了转发式测量模型,并给出了转发式测定轨新系统对GEO卫星和北斗IGSO卫星(I1-S)的测定轨结果.经过试验验证,GEO、IGSO卫星的重叠弧段的轨道差的RMS值已分别达到2m和0.9in.长期的试验应用和分析表明,转发式测定轨技术的主要特色和优越性在于:转发测距与钟差分离,便于实现精密定轨;以精密时间测量为基础,测距精度高(2cm),并且不受气象条件制约;使用微波频段和扩频技术,易于远距离测轨;该技术所需的星上透明转发器载荷成熟且易于小型化.从未来应用来看,转发式测定轨技术适用于中高轨航天器的精密测定轨,尤其对高轨卫星测定轨有明显优势,可用于开展相关科学研究.

The observation data in the B band for BL Lacerate object PKS 0735+178 during 1970–1998 from twenty two publications have been compiled into a light curve. The light curve shows that PKS 0735+178 is very active and exhibits very complicated non-sinusoidal variations. Using both Jurkevich's method and Power spectrum method to analyze these data we have found two periods of 5.26±0.98 years and 1.24±0.05 years for the outbursts in PKS 0735+178. It is of interest to note that the results of the two methods are the same (almost). In addition, these values are in good agreement with the results found by Smith et al.47 and Webb et al.61 We also apply the binary black hole model to explain the central structure of this object and obtain the masses of the primary and secondary black holes are 1.7×109M⊙ and 2.88×107M⊙ respectively. It should be monitored in future to obtain more data for further analysis to test the hypothesis.

In this paper, we have collected the available observation data of BL Lac S5 0716+714 in I-band from published literature during 1994 to 2000. The light curve shows S5 0716+714 is very active and very complicated non-sinusoidal variations. We studied its medium-timescale periodicity using the Jurkevich and power spectrum method to search for the possible medium-timescale periods and found that one possible medium-timescale periodic with a period of around 14+/-0.1 day is obtained for S5 0716+714. It is interesting to note that these results are in good agreement with the previous results by Impey et al. (2000) and Qian et al. (2002), and this work provides a new analysis and evidence of the medium-timescale periodicity in BL Lac S5 0716+714. The helical jet model seems to be more reasonable for explaining our results than other models.

In this paper, we introduce a new composite spectral indices αγxγ = αxγ - αγ, and prove [Formula: see text], that means αγxγ is intrinsic. We plot a αxox - αγxγ diagram for 25 Gev γ-ray blazars for which αx and αγ have been provided in the literature, where αxox = αox - αx which was introduced by Sambruna et al. (1996) and proved that it is intrinsic by our previous paper (Xie et al. 2001). Using this new composite color–color (αxox - αγxγ) diagram, we investigated the nature of the HBLs–LBLs relationship, and the BL Lacs–FSRQs relationship, in high-energy emission. The results show that the spectral energy distributions of three subclasses of Gev γ-ray loud blazars are different, but essentially continuous: HBLs and FSRQs occupy separated regions while LBLs bridge the gap between HBLs and FSRQs. The results are consistent with that derived from a low energy color–color(αxox - αoro) diagram by Sambruna et al. (1996) and Xie et al. (2001). However, on the αox - αxγ diagram, FSRQs, LBLs and HBLs occupy same region. Because both αγxγ and αxox are intrinsic, thus, the new connection among HBLs, LBLs and FSRQs obtained by us is intrinsic.