The optical variability of flat-spectrum radio quasars in the SDSS stripe 82 region

• Published in: Astronomy and astrophysics (Berlin) Vol. 528; p. A95
• Main Authors: Gu, M.-F., Ai, Y. L.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.04.2011
• Subjects: Accretion disks; Astronomy; Blazars; Earth, ocean, space; Exact sciences and technology; galaxies: active; galaxies: photometry; Quasars; quasars: general; Radio; Spectra; Thermal emission; Trends; Active galaxies; Quasars; quasars: general; galaxies: active; Variability; galaxies: photometry; Spectral index; Blazar; Accretion disks; Radio spectrum; Photometry
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201016280

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.