Spectral Variation of NLS1 Galaxy PMN J0948+0022

Four well-sampled spectral energy distributions (SEDs) of PMN J0948+0022 are fitted with the syn+SSC+EC model to derive the physical parameters of its jets and to investigate the spectral variations of its SEDs. A tentative correlation between the peak luminosity (L_c) and peak frequency (ν_c) of its inverse Compton (IC) bump is found in both the observer and co-moving frames, indicating that the variations of luminosity are accompanied by the spectral shift. A correlation between L_c and δ is found, and thus the magnification of external photon field by the bulk motion of the radiation regions is an essential reason for the spectral variation since, IC bump of PMN J0948+0022 is dominated by the EC process.