SIMBAD references

We present the results of optical photometric (BVRI) monitoring of three gamma-ray-loud BL Lac objects (3C 66A, PKS 0735+178, and BL Lacertae) in 1999-2002. During our observations, these objects showed significant rapid variations: 3C 66A and PKS 0735+178 exhibit short-timescale (∼1 hr) variability in the B band, and BL Lac exhibits intraday variability in B and V. We find that there is a strong correlation between brightness and color for 3C 66A and BL Lac. We have analyzed the relationship between optical variability and gamma-ray variability and discuss theoretical models for gamma-ray-loud BL Lac emission. We have found shorter time variability for 3C 66A and PKS 0735+178 compared with previous reports.