Observational Study Of Intraday Variability Of The BL Lac Objects In X-ray High State

Blazars are a subclass of active galactic nuclei with their relativistic jets almost coincide with the observer's line of sight.The jets are wide believed to be generated by extracting the rotating energy of supermassive black holes.Due to the relativistic beaming effect of the jets,blazars have the characteristics of intra-day variability in multi-bands,polarization,superluminal speed and so on.Blazars can be divided into BL Lacs and FQSRs according to their spectral slopes.The Blazars'spectral-energy-distribution from radio to high energy are typically double-peaked.The low-energy radiation peaked from radio to ultraviolet or X-ray is generated by synchrotron radiation from relativistic electrons,while the high-energy radiation peaked from X-ray to gamma ray by inverse Compton scattering.Under the present observation capability,the relativistic jets of BL Lac objects are indistinguishable in all the electromagnetic bands except for in radio.Therefore,joint observation in multi-wave bands,especially in the burst state,is the only method to study the physical process of BL Lac objects.In this thesis,we used the GWAC-F60A telescope funded by Guangxi University to carry out quasi-simultaneous ground-based multi-band monitoring of three BL Lacs(1ES 0647+250,1ES 1218+304 and B2 1811+31)when they burst in X-ray band.We use~2-test and ANOVA test to check intra-day variability;Their variability behavior in colors is analyzed.The relative time delay between different bands is obtained based upon Z-transform discrete correlation function.The results can be described as follows.For the source 1ES 1218+304,both tests show that intra-day light variation is universal,and the shortest time scale of light variation is 27 minutes;For five days,the color change behavior is brighter and bluer,which is consistent with the expectation of the shock-in-jet model.There is a time delay in six days,the shortest delay is about 1.5 minutes and the longest is 10 minutes.A possible quasi-periodic oscillation has been detected.For B2 1811+31,although the intra-day variability is detected to be chromatic phenomenon was opposite.There is a time delay of 3 minutes in the first day.For 1ES 0647+250,the test suggest that intra-day variability can be identified in four days,in which a chromatic variation being brighter when bluer can be detected in three of the four days.