Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst

Abstract

The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. A predicted optical outburst was observed in late 2006/early 2007. We here present the radio-to-optical WEBT light curves during the outburst, together with UV data acquired by Swift in the same period. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of 5 mag led to the outburst peak in February 19-21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some shutdown mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin.

9 pages, 7 figures, in press for Astronomy and Astrophysics

References in corpus (8)

• The WEBT Campaign on the Blazar 3C279 in 2006
• Multifrequency variability of the blazar AO 0235+164. The WEBT campaign in 2004-2005 and long-term SED analysis
• Structure and flux variability in the VLBI jet of BL Lacertae during the WEBT campaigns (1995--2004)
• Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst
• Multi-frequency monitoring of gamma-ray loud blazars: I. Light curves and spectral energy distributions
• Spectroscopic monitoring of the BL Lac object AO 0235+164
• X-ray emission from the blazar AO 0235+16: the XMM-Newton and Chandra point of view
• Color Variability of the Blazar AO 0235+16

Cited by in corpus (16)

• Radio/gamma-ray time delay in the parsec-scale cores of active galactic nuclei
• Optical Intra-day Variability in Blazars
• A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008
• Multi-wavelength observations of blazar AO 0235+164 in the 2008-2009 flaring state
• Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst
• The high activity of 3C 454.3 in autumn 2007. Monitoring by the WEBT during the AGILE detection
• Comprehensive Monitoring of Gamma-ray Bright Blazars. I. Statistical Study of Optical, X-ray, and Gamma-ray Spectral Slopes
• Quasi-Periodic Oscillations in the long term radio light curves of the blazar AO 0235+164
• Long term optical and infrared variability characteristics of Fermi Blazars
• Detection of a quasi-periodic oscillation in the optical light curve of the remarkable blazar AO 0235+164
• The Variability and Period Analysis for the BL Lac AO 0235+164
• The variability of blazars throughout the electromagnetic spectrum
• Multiwavelength variability of the blazar AO 0235+164
• The Repeating Flaring Activity of Blazar AO 0235+164
• Study of variability in long-term multiwavelength optical lightcurves of blazar AO 0235+164
• Parsec-scale jet precession and a putative supermassive binary black hole system in the blazar AO 0235+164