We present a spectral analysis for a sample of redshift-known gamma-ray bursts (GRBs) observedwith Fermi/GBM. Together with the results derived from our systematical spectral energy distribution modeling with the leptonic models for a Fermi/LAT blazar sample, we compare the distributions of the GRBs and the blazars by plotting the synchrotron peak luminosity (Ls) and the corresponding peak photon energy Es of blazars in the Lp–Ep plane of GRBs, where Lp and Ep are the peak luminosity and peak photon energy of the GRB time-integrated νFν spectrum, respectively. The GRBs are in the high-Lp, high-Ep corner of the plane and a tight Lp–Ep relation is found, i.e., Lp ∝ Ep^(2.13+0.54−0.46). Both flat spectrum radio quasars (FSRQs) and low-synchrotron peaking BL Lac objects (LBLs) are clustered in the low-Ep, low-Lp corner. Intermediate- and high-synchrotron peaking BL Lac objects (IBLs and HBLs) have Es ∼ 2 × 10^(−3)–100 keV and Ls ∼ 10^(44)–10^(47) erg s−1, but no dependence of Ls on Es is found. We show that the tight Lp–Ep relation of GRBs is potentially explained with the synchrotron radiation of fast-cooling electrons in a highly magnetized ejecta, and the weak anti-correlation of Ls–Es for FSRQs and LBLs may be attributed to synchrotron radiation of slow-cooling electrons in a moderately magnetized ejecta. The distributions of IBLs and HBLs in the Lp–Ep plane may be interpreted with synchrotron radiation of fast-cooling electrons in a matter-dominated ejecta. These results may present a unified picture for the radiation physics of relativistic jets in GRBs and blazars within the framework of the leptonic synchrotron radiation models. 

 By for with WU Xuefeng