Zhang, You-Hong; Bian, Fuyan; Li, Jun-Zheng; Shang, Ren-Cheng
We present optical observations of BL Lacertae (BL Lac) in the standard BVRI bands with the 80 cm Tsinghua Centre for Astrophysics-National Astronomical Observatories of China telescope. In 2004, BL Lac was monitored for 25 nights, between September and November, to study its long-term optical variability behaviour. The source initially faded by δR ~ 1 mag in ~30 d and then brightened by δR ~ 0.8 mag in ~20 d. It was further monitoredfor six consecutive nights on 2005 September 3-8, focusing on...[Show more]
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