Gamma‐Ray and Multi–Wave Band Emission from Gamma‐Ray–loud Blazars

Using multi-wave band data for 61 γ-ray-loud blazars (17 BL Lacertae objects and 44 flat-spectrum radio quasars [FSRQs]), we have studied the possible correlation between flux densities ( F R , F K , F O , F X , and F γ ) in the radio, infrared, optical, X-ray, and γ-ray wave bands, in both the low and high states. For some blazars, it is hard to determine whether they are in a low or a high state because only one data point is available for each of them; initially, we exclude these blazars in our analysis. However, we include these blazars in later analysis by temporarily assuming them to be in a low state or a high state. Our main results are as follows. There are very strong correlations between F X and F O and between F O and F K in both low and high states. However, a strong correlation between F X and F K exists only in the low state. No definite correlation is found between γ-ray flux density and those of lower energy bands; however, there are hints of anticorrelation between F γ and F X as well as F γ and F O and a positive correlation between F γ and F R . From these results we suggest that (1) photons from infrared to X-rays are emitted by the same particles via synchrotron radiation and (2) if γ-rays are mainly produced by an inverse Compton scattering mechanism, it seems that the up-scattered soft photons are from external photons rather than synchrotron photons.