The Relations of Multi-waveband Effective Spectral Indices for Fermi Blazars

In this paper, the flux densities at the radio (R) 1.4GHz, optical (O) 4.68 × 1014Hz, X-ray (X) 1keV, and γ-ray (γ) 1GeV are obtained from the available literature for a Fermi blazar sample. The 6 effective spectral indices (αRO, αRX, αRγ, αOX, αOγ, and αXγ) between any two of above bands are calculated. The correlations between any two spectral indices are investigated for the whole blazar sample and the subclass samples of FSRQs (Flat Spectral Radio Quasars) and BL Lacs including High synchrotron peak frequency BL Lacs (HBLs) and Low synchrotron peak frequency BL Lacs (LBLs). Results show that: (1) There are close correlations between any two spectral indices for all samples, except for the sample of HBLs and the correlation between αOX and αRγ. This kind of correlations can be explained by the structures of energy spectral distributions at four bands. (2) In the scatter plots of effective spectral index correlations, FSRQs and LBLs are distributed in the same area, but HBLs and FSRQs (LBLs) are distributed in the different areas. (3) The separation degree (discrimination) between the distributions of FSRQs (LBLs) and HBLs differs with the scatter plot of effective spectral index correlations, and the discrimination is related to the frequencies to determine two effective spectral indices.