Long-term optical and radio variability analysis of BL Lacertae 2200+420

Based on the radio light curves in 22 GHz and 37 GHz from the Metsahovi monitoring program and the optical light curves in BVRI bands from previously published results and the"Whole Earth Blazar Telescope"(WEBT)archives,we analyze the time delay among 22 GHz,37 GHz and optical bands(B,V,R,I)of BL Lacertae by means of discrete correlation method.The results suggest there exist strong correlation among 22 GHz,37 GHz and optical bands(B,V,R,I)with zero-lag.The 37 GHz lags behind R band by 11 months.The correlation of brightness and color index among BVRI bands,brightness and spectral index between 37GHz and 22 GHz are also investigated.The results show a clear trend of bluer-when-brighter.     

耀变体S5 0716+714的混沌特性研究

长期观测显示,耀变体S5 0716+714具有复杂的光变行为.本文运用混沌理论,研究了S5 0716+714四个较大爆发阶段的射电、光学和X波段的光变曲线.分别计算了它们的关联维和Lyapunov指数.结果表明:1)光变曲线的关联维和Lyapunov指数都介于纯混沌系统与随机噪声之间;2)相轨迹是一个与Rossler吸引子相似的混沌系统,由于受到各种内在或外在因素的影响产生噪声,导致关联维和Lyapunov指数均比Rossler吸引子大,相轨迹出现紊乱.从这两个混沌判据上看,三个波段均表现出很强的混沌特性,因此推断S50714+716的光变是一个混沌现象.     

Searching for axion-like particles with the blazar observations of MAGIC and Fermi-LAT

In this study, we explore the axion-like particle (ALP)-photon oscillation effect in the γ-ray spectra of the blazars Markarian 421 (Mrk 421) and PG 1553+113, which are measured by the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) and Fermi Large Area Telescope (Fermi-LAT) with high precision. The Mrk 421 and PG 1553+113 observations of 15 and five phases are used in the analysis, respectively. We find that the combined analysis with all the 15 phases improves the limits of the Mrk 421 observations. For the selected blazar jet magnetic field and extragalactic background light models, the combined limit set by the Mrk 421 observations excludes the ALP parameter region with the ALP-photon coupling of \begin{document}$g_{a\gamma} \gtrsim 2 \times 10^{-11} \; {\rm GeV}^{-1}$\end{document} for the ALP mass of \begin{document}$ \sim 8\times 10^{-9} \lesssim m_a \lesssim 2\times 10^{-7}\rm \; eV $\end{document} at 95% confidence level. The main uncertainties of the analysis originate from the blazar jet magnetic field model. We also find that the ALP hypothesis can slightly improve the fit to the PG 1553+113 results in several parameter regions. We do not set the limit in this case.