Abstract Using the HST observation data of BL Lac objects by Urry et al. and γ-ray observation data, we find that there is a correlation between Fγ and FOnuclei for γ-ray-loud BL Lac objects (correlation coefficients: γ = 0.63, p = 4.0 ×10-2), but no correlation between Fγ and Fhost, where FOnuclei and FOhost are the fluxes of nuclei and host galaxy in V-band. For 19 γ-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 αγ and αK for 15 BL Lac objects ( γ = 0.84, p = 3.11× 10-4); (2) the correlation between αγ and αO for 12 BL Lac objects is γ = 0.82, p = 1.5 × 10-3; (3) there is no correlation between αγ and αX 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 γ-ray emission of the BL Lac objects. The electrons emitting IR and optical radiation via synchrotron are also responsible for upscattering these photons to γ-rays, and a variability in IR-optical regime should be accompanied by a change in the γ-rays.

Keywords gamma rays --- BL Lacertae objects: general

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