Properties Of High Energy Radiation In TeV BL Lacs And Constrain Of Their Redshift

Blazar,a special subclass of active galaxy nuclei(AGNs),are the centers of galaxies with violent activities.So far,almost all identified GeV-TeV AGNs are BL Lacs,their radiation mechanism can be well described as a one-zone synchrotron+synchrotron-self-Compton(SSC)model.However,for some TeV Blazars,especially for BL Lac objects,their spectral energy distributions(SEDs)require extreme value of parameters based on the SSC model.To find out those objects enable us to go further research.In addition,since the launch of the space-based and ground-based telescopes,we have the opportunity to get the(quasi-)simultaneous multi-waveband SEDs and study the properties of the BL Lacs by fitting the SEDs directly.Furthermore,the BL Lacs,as the end of the Blazar sequence,to study the emission mechanism and research the model of the extragalactic background light(EBL),their statistical study of physical properties are needed.In this thesis we present the systematic analysis of the physical properties of the GeV-TeV BL Lacs and the method to constrain the reddhifts of TeV BL Lacs.(1)Using the Markov Chain Monte Carlo(MCMC)method to study a sam-ple of GeV-TeV BL Lacs.The BL Lac objects are thought to be old quasars with weak or no external seed photons plus an inefficient accretion disk,their SEDs suffer less contamination by external photons and give us an opportunity to explore the intrinsic physical properties of emitting region as well as the jet.In this paper,we fit the SEDs of 46 GeV-TeV BL Lac objects in the frame of leptonic one-zone synchrotron self-Compton(SSC)model and investigate the physical properties of these objects.We use the Markov Chain Monte Carlo(MCMC)method to obtain the basic parameters,such as magnetic field(B),the break energy of the relativistic electron distribution(?'b)and the electron energy spectral index?Based on the modeling results,as well as the mass of the black hole derived from the literature,we analyze the distributions of the parameters,the accretion ratio and the physical properties of the jet.we also check the so called the blazar sequence and propose that this sequence does exist.Further-more,the structure of jet may have two sub-structures,namely,a fast core with a slow sheath.This peculiar structure may maintain a steady state if the magnetic field is stronger enough,then leading to the rare micro-variability in the optical bands.At lest,from our results,we find that several objects with extreme pa-rameters especially for the Doppler factor(?50),which disfavors the observation taken by VLBI.This result calls for the further work to study.(2)For BL Lacs without line emission spectrum,its redshift is hard to be obtained directly.VHE(? 100 GeV)photons emitted by BL Lacs are effectively absorbed by interacting with the EBL.Motivated by this mechanism,we propose a method that use a reliable EBL model to estimate the redshift of TeV BL Lac object.In this method,the redshift is a parameter and the SEDs from optical to GeV band are fitted with one-zone SSC model,then the model SED is extrapolated into the TeV band.This extrapolation is modified by the EBL absorption which only depends on the redshift if the cosmological parameters are given.Comparing the absorbed spectrum with the observed one,we can estimate the redshift z.In the fitting procedure,the MCMC method is used to explore the parameter space.Based on this method,the quasi-simultaneous multi-waveband SEDs of three BL Lacs,observed by Ultraviolet and Optical telescope(OVIO),KVA 60 cm telescope,Swift X-Ray telescope,Fermi/LAT,MAGIC telescopes,H.E.S.S and VERITAS are fitted.However,in the SSC model,the electron energy distributions(EED)is important to determine the SEDs,and indicates the acceleration and cooling processes of electrons in the jet.In this paper,three types of EEDs,a power-law with exponential cut-off(PLC),a log-parabola(PLLP)and a broken power-law(BPL)are adopted.We show that the EEDs might change the shape of SEDs and then lead to the different redshift.In addition,the EBL models are linked with the absorption of TeV photons,so we use a normalization factor ? to scale the uncertainties of the EBL models.Furthermore,We apply our method to obtain the red shifts of three TeV BL Lac objects in the marginalized 68 per cent confidence,and find that the PLC EED does not fit the SEDs.For 3C 66A,the red shift is 0.14-0.31 and 0.16-0.32 in the BPL and PLLP EEDs.For PKS 1424+240.the red shift is 0.55-0.68 and 0.55-0.67 in the BPL and PLLP EEDs.For PG 1553+113,the red shift is 0.22-0.48 and 0.22-0.39 in the BPL and PLLP EEDs.We also estimate the red shift of PKS 1424+240 in the high stage to be 0.46-0.67 in the PLLP EED,roughly consistent with that in the low stage.