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Issue A&A
Volume 369, Number 3, April III 2001
Page(s) 758 - 762
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010169



A&A 369, 758-762 (2001)
DOI: 10.1051/0004-6361:20010169

Optical observations of BL Lacertae from 1997 to 1999

J. H. Fan1, 2, 3, B. C. Qian4 and J. Tao4

1  Center for Astrophysics, Guangzhou University, Guangzhou 510400, PR China,
2  Chinese Academy of Science-Peking University Joint Beijing Astrophysical Center (CAS-PKU.BAC), Beijing, PR China
3  Department of Physics, Yunnan University, Kunming, PR China
4  Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, PR China

(Received 2 May 2000 / Accepted 9 January 2001)

Abstract
We present the optical (V, R, and I) photometry for BL Lacertae, which was observed from 1997 through 1999, with the 1.56-m telescope at the Shanghai astronomical observatory (SHAO). After the 1997 outburst, it dimmed to a low state and then brightened again. During the period JD 2450701 to JD 2450701.5, variations of 0.40 mag, 0.27 mag, and 0.21 mag over a time scale of 100 min were found for V, R, and I bands, suggesting that the variations were decreasing with wavelength. The correlation between V, R, and I is also analyzed using the DCF (Discrete Correlation Function) method. This shows that the variability in the V, R, and I bands are correlated with no time delay longer than 0.2 day. galaxies: active; BL Lacertae objects: individual: BL Lac (PKS 2200+420); galaxies: photometry


Offprint request: J. H. Fan, jhfan@guangztc.edu.cn

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