Jet And Variability From Fermi Blazar

Since the launch of the Fermi Large Area Telescope（LAT）, we have entered in a new era of blazars research. The blazars detected by Fermi LAT have also been observed by many different wavelengths of telescopes. These observations promote our understanding about nature of blazars, origin of high energy gammaray, accretion models, and composition, generation, transmission and acceleration of jet. In this dissertation, the main research contents are following: relationships among jet power, black hole mass and accretion disk, basic properties of Fermi blazars, blazar sequence and optical variability of blazar. The background and meaning of active galactic nuclei（AGN）, blazar, blazar detected by Fermi LAT, relativistic jet, relations between jet and accretion, blazar sequence and variability are reviewed in Chapter 1. My own research works are presented in Chapters 2-5. The most important results of these research works are: there are significant correlations between jet power and black hole mass, between jet power and Eddington ratio; Fermi blazars are likely to have a more powerful jet and beaming effect; the relationship between jet power and synchrotron peak frequency corrected by beaming effect supports the blazar sequence and unification of blazars and radio galaxies; long term optical monitoring results show that Mrk 501 has variabilities for optical flux and color indices on different timescales,which supports the shock-in-jet model, specifically as follows.In Chapter 2, we have analyzed a large sample of clean blazars detected by Fermi LAT. Using literature and calculation, we obtained intrinsic γ-ray luminosity excluding beaming effect, black hole mass, broad-line luminosity（used as a proxy for disk luminosity）, jet kinetic power from “cavity” power and bulk Lorentz factor for parsec-scale radio emission, and studied the distributions of these parameters and relations between them. Our main results are as follows.（i）After excluding beaming effect, intrinsic γ-ray luminosity with broad line luminosity, black hole mass and Eddington ratio have significant correlations. Our results confirm the physical distinction between BL Lacs and FSRQs.（ii） The cor-relation between broad line luminosity and jet power is significant which supports that jet power has a close link with accretion. Jet power depends on both the Eddington ratio and black hole mass. We also obtain log L_BLR～（0.98 ± 0.07）log P_jet for all blazars, which is consistent with the theoretical predicted coefficient.（iii） For almost all BL Lacs, P_jet> L_disk; for most of FSRQs, P_jet< L_disk. The“jet-dominance”（parameterized as （?）） is mainly controlled by the bolometric luminosity.In Chapter 3, by statistically analyzing a large sample which includes blazars of Fermi detection（FBs） and non-Fermi detection（NFBs）, we find that there are significant differences between FBs and NFBs for redshift, black hole mass, jet kinetic power from “cavity” power, broad-line luminosity, and ratio of core luminosity to absolute V-band magnitude（R_v）, but not for ratio of radio core to extended flux（R_c） and Eddington ratio. Compared with NFBs, FBs have larger mean jet power, R_c and R_v while smaller mean redshift, black hole mass, broadline luminosity. These results support that the beaming effect is main reason for differences between FBs and NFBs, and that FBs are likely to have a more powerful jet. For both Fermi and non-Fermi blazars, there are significant correlations between jet power and the accretion rate（traced by the broad-emission-lines luminosity）, between jet power and black hole mass; for Fermi blazars, the black hole mass does not have significant influence on jet power while for non-Fermi blazars, both accretion rate and black hole mass have contributions to the jet power.In Chapter 4, based on a large Fermi blazar sample, the blazar sequence(synchrotron peak frequency ν_peak versus synchrotron peak luminosity L_peak) is revisited. It is found that there is significant anti-correlation between ν_peak and L_peak for blazars. However, after being Doppler corrected, the anti-correlation disappears. The jet cavity power(P_jet) is estimated from extended radio luminosity.So it is free of beaming effect. We find that there are significant anti-correlations between P_jet and beam-corrected ν′_peak for both blazars and radio galaxies, which supports the blazar sequence and unification of blazars and radio galaxies（an alternative relationship is the correlation between jet power and γ-ray photon index）.In Chapter 5, we used the 1.02 m optical telescope located at the the Yunnan Astronomical Observatory（YAO） of China to monitor the BL Lac object Mrk 501 in optical V, R and I bands from 2010 to 2015. For Mrk 501, the presence of strong host galaxy component can affect the results of photometry.After subtracting the host galaxy contributions, the source shows intraday and long-term variabilities for optical flux and color indices. The average variability amplitudes of V, R and I bands are 22.05%, 22.25%, 23.82% respectively, and the value of duty cycle 14.87 per cent. A minimal variability timescale of 106 minutes is detected. No significant time lag between V and I bands is found on one night. The bluer-when-brighter（BWB） trend is dominant for Mrk 501 on intermediate, short and intraday timescales which supports the shock-in-jet model. For the long timescale, Mrk 501 in different state can have different BWB trend.