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.
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 mediumtimescale 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.
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.
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