Radio spectral index of BL Lac objects

In this paper, the preliminary data from University of Michigan Radio Astronomy Observatory database (UMRAO) are used to discuss the radio spectral index properties of 8 BL Lacs. To do so, we calculated the radio spectral index, alpha (F ae nu (alpha) ), which was obtained by fitting the averaged flux densities in the bands (4.8 GHZ, 8 GHz, and 14.5 GHz) by binning the original for 7 d. We also calculated the time delay between the averaged lightcurves and the spectral variance. Our calculations and analysis give the following results. 1) The averaged logarithmic flux density at 8 GHz (logF) and the corresponding spectral index (alpha) have strong correlation for all the BL Lacs; 2) the lightcurves and the spectral variability have the similar profile for all the BL Lacs; 3) the lightcurves delay spectral variability for all sources but PKS 0735+178, with the delay time ranging from 31 d to 125 d.