Study on Color Index of the Fermi Blazars

In this paper, the optical bandflux and color index of 19 Fermi Blazars are corrected by modulating the flux base-level. By comparing the correlation between the color index and the magnitude before and after the correction, the effect of the Doppler factor on the color index change mechanism is studied. Studies show that: (1) only five sources show a clear BWB trend before the correction, and two sources show a clear RWB trend; (2) after the correction, nine sources show a clear BWB trend, and six sources show a weak BWB trend, only the color indices of 4 sources have no correlation with the magnitude; (3) The color change mechanism of about half of the sources is affected by the Doppler beamforming effect. After correction, the correlation between the color index and magnitude of these sources is enhanced; (4) The change of the Doppler factor may be the cause of the weakening of the BWB trend. By studying the correlation between the color index and the magnitude, the radiation mechanism of Blazars can be further explained.