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Blazar Anti-Sequence of Spectral Variation within individual Blazars: Cases for Mrk 501 and 3C 279

The jet properties of Mrk 501 and 3C 279 are derived by fitting the broadband spectral energy distributions with the lepton models. The derived gamma_b (the break Lorenz factor of the electron distribution) are 10^4-10^6 for Mrk 501 and 200~600 for 3C 279 and the magnetic field strength (B) of Mrk 501 is usually one order of magnitude lower than that of 3C 279, but their Doppler factors (delta) are comparable. A spectral variation feature that the peak luminosity is correlated with the peak frequency, which is opposite to the blazar sequence, is observed in the two sources. We find that (1) the peak luminosities of the two bumps in SEDs for Mrk 501 depend on gamma_b in both the observer and co-moving frames, but they are not correlated with B and delta; (2)the luminosity variation of 3C 279 is dominated by the external Compton (EC) peak and its peak luminosity is correlated with gamma_b and delta, but anti-correlated with B. These results suggest that gamma_b may govern the spectral variation of Mrk 501 and delta and B would be responsible for the spectral variation of 3C 279. The narrow distribution of gamma_b and the correlation of gamma_b and B in 3C 279 would be due to the cooling by the EC process and the strong magnetic field. Based on our brief discussion, we propose that this spectral variation feature may be originated from the instability of the corona but not from the variation of the accretion rate as that for the blazar sequence.