The Jet Emission In GeV Narrow-line Seyfert 1 Galaxies

Active galactic nuclei(AGNs)are among the most spectacular objects in the sky.Because of their violent activities,they can be the natural laboratories for extreme physical phenomena which we would like to learn.The study of active galactic nuclei can help us understand the evolution of the local Universe,the formation and evolution of galaxies.In this thesis,I will introduce the observational progress and the basic model of AGNs.And then,I will report my works about GeV narrow-line Seyfert 1 galaxies(NLSls).Up to now,the number of GeV NLSls detected by Fermi/LAT has increased to 7,they are 1H 0323+342,PMN J0948+0022,SBS 0846+513,PKS 1502+036,PKS 2004-447,FBQS J1644+2619 and SDSS J122222.55+041315.7.We analyse their LAT data retrieved from the Fermi Science Support Center using the standard procedures described on the website.The results show that there is no apparent correlation between their luminosity and spectrum index,expect for SBS 0846+513.In order to have a further study of its spectral evolution,we separate the 7-years light curves of SBS 0846+513 into three episodes.It is found that the correlation holds and becomes stronger.Therefore,the origin of y-ray for SBS 0846+513 may be different from the others,and the seed photon of inverse-Compton scattering may be from the dusty torus.There are many evidence that the jet radiation of flat spectrum radio quasars is similar to that of GeV narrow-line Seyfert 1 galaxies.With one-zone leptonic models,we model the broadband spectral energy distributions(SEDs)of 3C 279(FSRQ)and PMN J0948+0022 and 1H0323+342 in different flux stages.The results show that their Doppler factors and peak luminosities(Lc,peak luminosity of external Compton scattering bumps)follow a universal correlation.Through an acombined sample including FSRQs and GeV NLS1 s,it is found that the same ?-Lc correlation holds,and it may imply a unified picture of the cooling mechanisms and particle acceleration in the comoving frame for NLSls and FSRQs.This also shows that the variations of observed luminosities may be due to the Doppler boosting effect.In addition,when we replace Lc with LLAT which is the luminosity observed by Fermi/LAT,the correlation holds.And we can use this tight correlation to estimate the Doppler factors ? using the observed luminosity in the Fermi/LAT band(LLAAT).The ? values we estimate with our method are consistent with the values derived by other methods.