Volume 528, April 2011
|Number of page(s)||8|
|Published online||08 March 2011|
The optical variability of flat-spectrum radio quasars in the SDSS stripe 82 region
Key Laboratory for Research in Galaxies and Cosmology, Shanghai
Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, 200030
2 Department of Physics, University of California, Santa Barbara, CA 93106, USA
3 National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, Yunnan, PR China
4 Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, Yunnan, PR China
Accepted: 10 January 2011
Context. Although a bluer-when-brighter trend is commonly observed in blazars, the opposite trend of redder-when-brighter has also been found in some blazars.
Aims. We investigate the frequency of the redder-when-brighter trend in flat-spectrum radio quasars (FSRQs).
Methods. We investigate the optical variability of 29 FSRQs in the SDSS Stripe 82 region using SDSS DR7 released multi-epoch data covering about nine years. We determined the spectral index by fitting a powerlaw to SDSS ugriz photometric data, and explored the relationship between the spectral index and source brightness.
Results. For all FSRQs studied, we detect variations in r band flux of overall amplitude between 0.24 mag and 3.46 mag in different sources. Fourteen of 29 FSRQs display a bluer-when-brighter trend. However, only one source exhibits a redder-when-brighter trend, which implies that this behavior is rare in our FSRQ sample. In this source, the thermal emission from the accretion disk may be responsible for the redder-when-brighter trend.
Key words: galaxies: active / quasars: general / galaxies: photometry
© ESO, 2011
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