Multi-color optical monitoring of ten blazars from 2005 to 2011

TL;DR

This study presents extensive multi-color optical monitoring of ten blazars over six years, revealing significant variability, color behaviors, and spectral properties, contributing a large dataset for understanding blazar emission mechanisms.

Contribution

It provides one of the largest optical datasets for ten blazars, analyzing long-term variability, color trends, and spectral indices with detailed observational data.

Findings

Most blazars showed significant variability.

BL Lac objects exhibited bluer-when-brighter chromatism.

No time delay was found between different wavelength variations.

Abstract

We carried out multi-color optical monitoring of a sample of ten blazars from 2005 to 2011. The sample contains 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. Our monitoring focused on the long-term variability and the sample included nine BL Lac objects and one flat-spectrum radio quasar. A total number of 14799 data points were collected. This is one of the largest optical database for a sample of ten blazars. All objects showed significant variability except OT 546. Because of the low sampling on each single night, only BL Lacertae was observed to have intra-day variability on 2006 November 6. Most BL Lac objects showed a bluer-when-brighter chromatism, while the flat-spectrum radio quasar, 3C 454.3, displayed a redder-when-brighter trend. The BWB color behaviors of most BL Lacs can be at least partly interpreted by the fact of increasing variation amplitude with increasing frequency observed in these objects. The average spectral index of LBLs is around 1.5, as expected from the model dominated by Synchrotron Self-Compton (SSC) loss. The optical emission of HBL is probably contaminated by the thermal emission from the host galaxies. Correlation analysis did not reveal any time delay between variations at different wavelengths.