A periodicity analysis of the radio light curves of the blazar NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved phase dispersion mini- mization technique. The result, which shows two persistent pe...A periodicity analysis of the radio light curves of the blazar NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved phase dispersion mini- mization technique. The result, which shows two persistent periodic components of 6 and ~ 10 yr at all three frequencies, is consistent with the results obtained with the Lomb-Scargle periodogram and weighted wavelet Z-transform algorithms. The reliability of the derived periodicities is confirmed by the Monte Carlo numerical sim- ulations which show a high statistical confidence. （Quasi-）Periodic fluctuations of the radio luminosity of NRAO 530 might be associated with the oscillations of the accre- tion disk triggered by hydrodynamic instabilities of the accreted flow.展开更多
The Swift/XRT light curve of the ultraluminous X-ray source NGC 5408 X-1 was re-analyzed with two new numerical approaches, the Weighted Wavelet Ztransform and CLEANest, and the results are different from previous stu...The Swift/XRT light curve of the ultraluminous X-ray source NGC 5408 X-1 was re-analyzed with two new numerical approaches, the Weighted Wavelet Ztransform and CLEANest, and the results are different from previous studies. Both techniques detected a prominent periodicity with a time scale of 115.5 ± 1.5 days, in excellent agreement with the detection of the same periodicity first reported by Strohmayer . Monte Carlo simulations were employed to test the statisitical confidence of the 115.5-day periodicity, yielding a statistical significance of 〉 99.98% （or 〉 3.8σ）. The robust detection of the 115.5-day quasi-periodic oscillations, if they are due to the orbital motion of the binary, would infer a mass of a few thousand M⊙ for the central black hole, implying there is an intermediate-mass black hole in NGC 5408 X-1.展开更多
基金supported by the National Basic Research Programof China (973 Program,2009CB24900)the Guangxi Natural Science Foundation (0991018Z)+3 种基金the Science and Technology Commission of Shanghai Municipality (06DZ22101)supported by a grant from the Chinese Academy of Sciencesa visitor grant from the The Netherlands Science Foundationsupported by funds from the NSF,NASA,and the University of Michigan
文摘A periodicity analysis of the radio light curves of the blazar NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved phase dispersion mini- mization technique. The result, which shows two persistent periodic components of 6 and ~ 10 yr at all three frequencies, is consistent with the results obtained with the Lomb-Scargle periodogram and weighted wavelet Z-transform algorithms. The reliability of the derived periodicities is confirmed by the Monte Carlo numerical sim- ulations which show a high statistical confidence. （Quasi-）Periodic fluctuations of the radio luminosity of NRAO 530 might be associated with the oscillations of the accre- tion disk triggered by hydrodynamic instabilities of the accreted flow.
基金partly supported by the National Basic Research Program of China(973 Program, Grant Nos. 2009CB24900 and 2013CB837901)the National Natural Science Foundation of China (Grant No. 61261017)+3 种基金the Strategic Priority Research Program of the CAS(XDA04060700)the China-Hungary Exchange Program of the CASthe Hungarian Scientific Research Fund (OTKA K104529) the Science & Technology Commission of Shanghai Municipality (06DZ22101)
文摘The Swift/XRT light curve of the ultraluminous X-ray source NGC 5408 X-1 was re-analyzed with two new numerical approaches, the Weighted Wavelet Ztransform and CLEANest, and the results are different from previous studies. Both techniques detected a prominent periodicity with a time scale of 115.5 ± 1.5 days, in excellent agreement with the detection of the same periodicity first reported by Strohmayer . Monte Carlo simulations were employed to test the statisitical confidence of the 115.5-day periodicity, yielding a statistical significance of 〉 99.98% （or 〉 3.8σ）. The robust detection of the 115.5-day quasi-periodic oscillations, if they are due to the orbital motion of the binary, would infer a mass of a few thousand M⊙ for the central black hole, implying there is an intermediate-mass black hole in NGC 5408 X-1.
