Gamma-ray and multi-wave band emission from gamma-ray-loud blazars

Using multi-wave band data for 61 gamma-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-gamma) in the radio, infrared, optical, X-ray, and gamma-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 gamma-ray Bur density and those of lower energy bands; however, there are hints of anticorrelation between F-gamma and F-X as well as F-gamma and F-O and a positive correlation between F-gamma 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 gamma-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.