Gamma-ray Emission from the γ-ray-loud BL Lac Objects

Abstract

Using the HST observation data of BL Lac objects by Urry et al. and gamma-ray observation data, we find that there is a correlation between Fgamma and F-O(nuclei) for gamma-ray-loud BL Lac objects (correlation coefficients: gamma = 0.63, p = 4.0 x 10(-2)), but no correlation between F-gamma and F-O(host), where F-O(nuclei) and F-O(host) are the fluxes of nuclei and host galaxy in V-band. For 19 gamma-ray-loud BL Lac objects with observed spectral index in multi-wavebands, the spectral index correlations between any two bands are as follow: (1) there is a strong correlation between alpha(gamma) and alpha(K) for 15 BL Lac objects (gamma = 0.84, p = 3.11 x 10(-4)); (2) the correlation between alpha(gamma) and alpha(O) for 12 BL Lac objects is gamma = 0.82, p = 1.5 x 10(-3); (3) there is no correlation between alpha(gamma), and alpha(x) for 16 BL Lac objects. The results, together with characteristic double-humped shape of their SEDs, show that the synchrotron self-Compton mechanism might be a main mechanism for the gamma-ray emission of the BL Lac objects. The electrons emitting IR and optical radiation via synchrotron are also responsible for upscattering these photons to gamma-rays, and a variability in IR-optical regime should be accompanied by a change in the gamma-rays.