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 \pm 0.11 } , 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 .