Study On Gamma-ray Properties Of Compact Symmetric Objects

Active galactic nuclei(AGNs)are the centers of galaxies with violent activities and physical processes.The activities of AGNs are powerful and are accompanied by significant variabilities at multiwavelength.The radiations of AGNs almost cover the entire electromagnetic spectrum from radio to gammaray bands.Compact symmetric objects(CSOs)are a sub-class of AGNs,characterized by a symmetric and sub-kiloparsec(sub-kpc)radio structure.Based on some observational and theoretical studies,CSOs are considered as young radio sources in the early stage of the evolution for AGNs,and a fraction of CSOs may evolve into the classical radio galaxies.At present,the related research progresses of CSOs are mainly in the radio to X-ray bands,while the gamma-ray band has not been fully studied.So far,the Fermi satellite's LAT detector has detected only five CSOs with gamma-ray radiation.In this paper,we use Fermi/LAT observational data to study the high-energy radiation properties and jet radiation characteristics of CSOs for understanding the jet properties at different evolutionary stages of AGNs.We firstly selected the brightest one with typical radio structure,CTD 135,among the gamma-ray emitting CSOs,and analyzed its ?11-year Fermi/LAT observational data.We found that its gamma-ray emission has high luminosity and shows significant variabilities.And a quasi-periodic oscillation(QPO)signal with a periodicity of ?460 days is detected in its gamma-ray light curve.Based on the two-zone lepton model,we found that the broadband spectral energy distribution(SED)of CTD 135 can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region,its gamma-rays are from the core region,which relativistically moves with a small viewing angle,being similar to blazar jets.These results are not coincident with its symmetric radio structure.Hence we proposed that an episodic jet exists in the core region of CTD 135.Its pc-scale lobes are remnants from the previous period of jet activity while its ?-rays originate from a relaunched relativistic jet.In addition,the jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio sources,indicating that its jet radiation may be also driven by the Eddington ratio.We also analyzed the Fermi/LAT observational data of the other four gammaray emitting CSOs.These CSOs present the different gamma-ray emission properties.PMN J1603-4904,NGC 3894 and TXS 0128+554 may be similar to CTD 135,and their gamma-ray emission may originate from the core,however,the gamma-ray emission of PKS 1718-649 may originate from the radio lobes.