Big Blue Bump in Seyfert Nuclei

Based on the nuclear magnitude in the optical, inferred from the decomposition of the high-resolution optical image of HST WFPC1/2, and the ultraviolet flux, observed by IUE, the power law spectral index(α)(Fν~ν^-α) of Big Blue Bump(BBB) emission is measured for the Seyfert galactic nuclei. The average value of them is -0.55, less than the value of composite spectral index(0.46) of SDSS, close to the expected value(-0.3) of the spectral index for classic accretion disk emission in the same spectral region. Compared to the α~T, the BBB spectral index, measured from the total emission of galaxy, the above index α has a lower value for most Seyfert objects in our sample, although still with a wider distribution. Additionally, we conjecture that some type Ⅱ Seyfert objects have abnormal decrease, compared to type Ⅰ, due to the ultraviolet emission of galactic disk without proper deduction from the total galactic emission.