| The number of blazars detected in the ?-ray band has risen sharply since the Fermi-Large Area Telescope(Fermi-LAT)became operational.Blazars became a main contributors to the extragalactic diffuse ?-ray background.However,there are still numbers of blazars that have not been detected by Fermi-LAT.And such blazars are called ?-ray quiet blazars.Due to the lack of observational data in the ?-ray band,it has attracted the attention of many scholars and studied it.In this thesis,we mainly study the possible reason why they are undetected by Fermi-LAT and the physical properties of ?-ray-quiet FSRQ jets.In the first chapter,we introduce the observed characteristics,classification,and unified model of active galactic nuclei.This gives us an idea of what an active galactic nuclei is and the main differences between blazars and other active galactic nuclei.In the second chapter,we introduce the observed characteristics and spectral energy distributions(SED)of blazars,which provides conditions for studying the radiation mechanism of blazar jets and establishing related physical models.In the third chapter,based on the lepton model,we introduce the radiation mechanism of blazar jets and the Markov chain Monte Carlo method for obtaining the best fitting parameters.Based on the basic theories and research methods of the first three chapters,the concrete work is described in chapter 4.We collect 11 ?-ray-quiet FSRQs were selected as our sample,they with quasi-simultaneous multiwaveband data.By modelling their SEDs with the conventional one-zone leptonic model,we study physical properties of ?-ray-quiet FSRQ's jet and the possible reason why they are undetected by Fermi-LAT.Through theoretical analysis and model fitting results,the parameters(the electron injection luminosity,the Doppler factor and the distance of the radiation region from the central super-massive black hole)that have a greater impact on the ?-ray flux and their effects on the fluxes of synchrotron,synchrotron self-Compton and external Compton radiation are obtained.By the Kolmogorov-Smirnov test,we found no significant difference between the synchrotron flux of ?-ray-quiet FSRQs and ?-rayloud FSRQs.Finally,our results suggest that the radiation region located relatively far away from the central super-massive black hole,which is more likely to be the reason why ?-ray-quiet FSRQs are undetected by Fermi-LAT.In addition,we discussed the possibility that multiple parameters jointly affect and ?? absorption result in ?-rayquiet FSRQ not being detected by Fermi-LAT.The results show that:(1)When ?-ray-quiet FSRQ has both a smaller Doppler factor and higher electron injection luminosity(or a stronger magnetic field),it can cause ?-ray-quiet FSRQ to be undetected in the ?-ray band;(2)If the jet's radiation of ?-ray-quiet FSRQ occurs in the hot corona region,? photons may be absorbed,which may result in the ?-ray-quiet FSRQ not being detected in the ?-ray band. |
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