In this paper, we use the quasi-simultaneous spectra of Fermi bright blazars
and Fermi detected narrow line Seyfert 1 (NLS1) to study the blazar sequence
and inverse Compton (IC) models. I. The synchrotron peak luminosities (L_{s})
significantly inverse correlate with the synchrotron peak frequencies
(\nu_{s}), L_{s}\propto\nu_{s}^{-0.44}, which is consistent with the blazar
sequence. In addition to the correlation, there are some blazars showing low
\nu_{s} and low L_{s}. To study the relation between these low \nu_{s} low
L_{s} blazars and the blazar sequence, we present correlations of the parameter
L_{s}\nu_{s}^{1/4} with the ratio of Compton to synchrotron peak frequencies
(r_{Cs}\equiv\nu_{C}/\nu_{s}) and with the ratio of Compton to synchrotron
luminosities (CD\equiv L_{C}/L_{s}). The results indicate that both
correlations are significant with a Pearson's probability for null correlation
of p=0.0218 and p=0.0286 respectively. This does not support the idea that the
low \nu_{s} low L_{s} blazars are sources with less beaming. Another
possibility, as suggested by Ghisellini & Tavecchio, is that these blazars have
relative lower black hole masses. To test this, we collect the black hole
masses of 30 blazars from archives, and find that the hole mass correlates with
the parameter L_{s}\nu_{s}^{0.44} (p=0.0344). Therefore, the black hole masses
of low \nu_{s} low L_{s} blazars are statistically small. The NLS1s are thought
to have lower black hole masses. We find that the four NLS1s detected by Fermi
have low \nu_{s} and low L_{s}. This supports the above result. II. The ratio
r_{Cs} correlates with CD significantly (p=0.00375). The external Compton (EC)
model can naturally explain this correlation, while synchrotron self Compton
(SSC) model can not. This agrees with the findings of many authors that the EC
process dominates the gamma-ray emission of Flat Spectrum Radio Quasars.Comment: 9 figures, accepted by Ap
