Journal Article

The long-term multiband optical observations and colour index for the quasar 3C 273

B. Z. Dai, X. H. Li, Z. M. Liu, B. K. Zhang, W. W. Na, Y. F. Wu, J. M. Hao, Y. Xiang, Z. J. Jiang and L. Zhang

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 3, pages 1181-1192
Published in print January 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2008.14137.x
The long-term multiband optical observations and colour index for the quasar 3C 273

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The long baseline simultaneous multiband (BVRI) observations of blazar 3C 273 are presented. We have made 758 optical multiband observations with the Yunnan Astronomical Observatory (YAO) 103 cm and Shanghai Astronomical Observatory (SHAO) 156 cm from 2003 January to 2005 April. In our observational campaign, the average colour indices are BV= 0.21, VR= 0.26 and RI= 0.31. The mean magnitudes in B, V, R and I are 12.895, 12.698, 12.441 and 12.139, respectively. The source is in a steady state over observational campaign. The correlations between colour index and brightness are discussed. We find that the correlations of BV versus B, VR versus V and RI versus R have significant negative correlation, while BV versus V, VR versus R and RI versus I have positive correlation. These strong correlations imply that the spectrum becomes bluer (flatter) when the source becomes brighter, and redden (softer) when the source fades both in intraday and long-term variability. The spectral evolution trends of 3C 273 are consistent with those of BL Lac objects.

Keywords: BL Lacertae objects: general; BL Lacertae objects: individual: 3C 273; galaxies: photometry

Journal Article.  5194 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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