The mass of the central black hole and the Doppler factor determined for the gamma-ray loud BL Lacertae object AO 0235+164

In this letter, we use the absorption effect of X-rays on the gamma-rays in the gamma-ray loud BL Lac object AO 0235+164 to constrain its central blac k hole mass, its Doppler factor, the propagation angle and the size of its gamma-ray emission region. We found M = (3.5-5.4) x10(8)M., delta = 1.33-1. 89, Phi = 34.4 degrees-31.7 degrees, and d = 102-93.3 R-g for the model-spe cific numerical factor lambda = 1.0-0.1. Our work differs from the others i n that we assume the beamed gamma-rays to come from a solid angle Omega rat her than from an isotropic distribution. Our results imply that the gamma-r ays are from a distance of similar to 6 x 10(15) cm.