Mkn501长期光变性质

Long-term Variability Properties for Mkn501

在R和I波段对Mkn 501进行了测光观测,并结合历史文献得到Mkn 501在近30年间的光学、红外和射电等多个波段的光变曲线;讨论了光变与色指数之间的关系,发现色指数(B—V)与(B—R)之间有强相关,相关系数r=0.73.利用DCF方法分析了多波段光变的相关性,发现B波段与4.8GHz和红外波段的光变存在一定的正相关,利用CLEANest方法对B波段的光变曲线进行频谱分析,结果表明Mkn 501的光变曲线存在2个可能的周期,即(10.06±0.04)年和(21.60±0.17)年.

The optical photometric observations at I, R pass bands are carried out for Mkn501 using the 1.56 meter optical telescopes at Shanghai Astronomical Observatory at Sheshan. Combining our new observations with the published optical data, we got its longterm optical light curves, for a time coverage of near 80 years. However, the densely sampled data are in about past 30 years. Based on the available optical and infrared data in the literature, we found that the maximum optical variations are ΔU = 0.57mag, ΔB = 1.31 mag, ΔV=1.17mag, ΔR = 0.98mag, ΔI = 1.51mag;ΔJ=2.37mag, ΔH = 1.67mag, and ΔK = 1.4 mag respectively. We also get color indexes and find that there is a clear corre- lation between color index （B - V） and （B - R） with a correlation coefficient of r = 0.73 and a chance probability p 〈 10-4. In addition, investigating the correlation between the source brightness and the spectral index, it is found that the spectrum becomes steep with the source dimming when the source is brighter than 13 mag., however, the spectrum flat- tens with the source becoming even fainter when the source is fainter than 13 mag.. This phenomenon is consistent with the case for 3C 279 Fan （1999）. For the past 30 years of optical B band observations, a data compensated discrete Fourier transform-DCDFT plus CLEAN, namely the CLEANest method is used, the analysis result shows that there are 7 strong period signs. Out of the 7 period, there are two strong long-term periods of （10.06 ± 0.04） years and （21.60±0.17） years. The long-term period is explained as the orbit of a binary black hole system （BBHS）. In 2000, Rieger ＆ Mannheim investigated the 23 day period found in the X-ray and the TeV light curves during the 1997 outburst, they found if there is a binary black hole system at the center of Mkn501 and the 23 day period is associated with the secondary black hole, then the BBHS will cause an orbit period of 6 to 14 years. Our 10.06 year period is consistent with their result. When the UMRAO data is adopted to the performance of the correlation between the optical and the radio band using a discrete correlation function （DCF） method, it is found that the variation in optical band leads the those in the radio and infrared bands by about 1.2 to 1.6 years and 0.5 years respectively. We think that these correlation should be analyzed via more observations.