Vol 21, No 8

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

Si-Si Sun, Hua-Li Li, Xing Yang, Jing Lü, Da-Wei Xu, Jing Wang


Abstract We here report a monitor of the BL Lac object 1ES 1218+304 in both B- and R-bands by the GWAC-F60A 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 χ2 -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 × 107M⊙ that is invalid.


Keywords BL Lacertae objects: general — BL Lacertae objects: individual (1ES1218+304) — galaxies: active — method: statistical

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