The Emission Model Of FSRQ3C454.3

Fermi Gamma-ray Space telescope (Fermi) with unprecedented accuracy has dis-covered the GeV spectral break in most FSRQs and low-energy synchrotron peak BL Lacs(LSP), and has provided considerably high-quality data for studying the flare of Blazars. So far, the reason for the spectral break in GeV band and the spectral variabil-ity of Blazars is still argumentive. Generally, the radiation from optical to y-ray band is come from a compact region, and the radio radiation originate in a larger scale region. For simplicity, the radio data is considered as the upper limit in one-zone model, which the larger region is not considered. In our model, we consider the effect of the radio emitting region on the high-energy y rays, and consistently construct a two-zone model to explain the GeV break and the multi-wavelength SED, which including radio, opti-cal/UV, X-ray, and y-ray energy bands. We can explain the multi-wavelength SED of different periods in the flare state.We have studied the simultaneous spectral energy distribution of the2009Decem-ber flare and of the quiescent state by constructing a model which has two emitting regions. The results are as follows.(1) We find that all the considered SED (before, during and after the luminosity peak) can be explained by a one-zone model involv-ing synchrotron self-Compton plus external Compton emission from an accretion disk and a broad-line region. X-rays is origin of synchrotron self-compton radiation and the dominant emission mechanism between30MeV and30GeV is dominated by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region and from the thermal accretion disk.(2) We can conclude that the flare of3C454.3gives support to the idea that the site of the high energy emitting region in relativistic jets changes, and it is likely that, when it is located closer to the back hole, the emitting region is more compact, and has a smaller Doppler factor and a greater magnetic field. The flare in2009December can be due to the variability of the Doppler factor of the high energy emitting region.(3) The y-rays come from inverse Compton scattering on the photons of the thermal accretion disk in the low flux state. This implies that the spectral index of optical/UV is same as the one of y-ray band.(4) The spectral softening above2GeV could be due to y-ray absorption via photon-photon pair production on the soft X-ray photon field of the radio emitting region.