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 nu_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 with the spectral shift. A correlation between L_c and delta is found, and thus the magnification of the external photon field by the bulk motion of the radiation regions is an essential reason for the spectral variation since the IC bump of PMN J0948+0022 is dominated by the EC process.