The intra-day optical monitoring of BL Lacerate object 1ES 1218+304 at its highest X-ray flux level

We here report a monitor of the BL Lac object 1 ES 1218+304 in both B-and R-bands by the GWAC-F60 A telescope in eight nights,when it was triggered to be at its highest X-ray flux in history by the VERITAS Observatory and Swift follow-ups.Both ANOVA and χ^(2)-test enable us to clearly reveal an intraday variability in optical wavelengths in seven out of the eight nights.A bluer-when-brighter chromatic relationship has been clearly identified in five out of the eight nights,which can be well explained by the shock-in-jet model.In addition,a quasi-periodic oscillation phenomenon in both bands could be tentatively identified in the first night.A positive delay between the two bands has been revealed in three out of the eight nights,and a negative one in the other nights.The identified minimum time delay enables us to estimate the MBH=2.8 × 10^(7) M_(⊙) that is invalid.