Multifrequency variability of the blazar AO 0235+164. The WEBT campaign in 2004-2005 and long-term SED analysis

Abstract

A huge multiwavelength campaign targeting the blazar AO 0235+164 was organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the variability properties of the source. Monitoring observations were carried out at cm and mm wavelengths, and in the near-IR and optical bands, while three pointings by the XMM-Newton satellite provided information on the X-ray and UV emission. We present the data acquired during the second observing season, 2004-2005, by 27 radio-to-optical telescopes. They reveal an increased near-IR and optical activity with respect to the previous season. Increased variability is also found at the higher radio frequencies, down to 15 GHz, but not at the lower ones. The radio (and optical) outburst predicted to peak around February-March 2004 on the basis of the previously observed 5-6 yr quasi-periodicity did not occur. The analysis of the optical light curves reveals now a longer characteristic time scale of 8 yr, which is also present in the radio data. The spectral energy distributions corresponding to the XMM-Newton observations performed during the WEBT campaign are compared with those pertaining to previous pointings of X-ray satellites. Bright, soft X-ray spectra can be described in terms of an extra component, which appears also when the source is faint through a hard UV spectrum and a curvature of the X-ray spectrum. Finally, there might be a correlation between the X-ray and optical bright states with a long time delay of about 5 yr, which would require a geometrical interpretation.

14 pages, 10 figures (8 included in the text and 2 PNG files), in press for A&A

References in corpus (4)

• Multi-colour optical monitoring of eight red blazars
• Structure and flux variability in the VLBI jet of BL Lacertae during the WEBT campaigns (1995--2004)
• XMM-Newton observations of a sample of gamma-ray loud active galactic nuclei
• X-ray emission from the blazar AO 0235+16: the XMM-Newton and Chandra point of view

Cited by in corpus (25)

• Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007
• Optical Intra-day Variability in Blazars
• The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
• The WEBT Campaign on the Blazar 3C279 in 2006
• 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
• Supermassive binary black holes among cosmic gamma-ray sources
• Multi-frequency monitoring of gamma-ray loud blazars: I. Light curves and spectral energy distributions
• AGILE detection of variable gamma-ray activity from the blazar S5 0716+714 in September-October 2007
• Spectroscopic monitoring of the BL Lac object AO 0235+164
• The nature of the intranight variability of radio-quiet quasars
• Multiwavelength periodicity search in a sample of $\gamma$-ray bright blazars
• Extreme photo-polarimetric behaviour of the blazar AO 0235+164
• 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
• A comprehensive study on the variation phenomena of AO 0235+164
• A statistical study of the optical spectral variability in gamma-ray blazars
• Simultaneous Swift and REM monitoring of the blazar PKS0537-441 in 2005
• A Compact Extreme Scattering Event Cloud Towards AO 0235+164
• Variability and evolution of the optical polarization of a sample of gamma-ray blazars
• Multiwavelength variability of the blazar AO 0235+164
• Study of variability in long-term multiwavelength optical lightcurves of blazar AO 0235+164
• Color Variability of the Blazar AO 0235+16
• Variability Study and Searching for QPOs with day-like periods in the blazar S5 0716+714 with TESS
• Parsec-scale jet precession and a putative supermassive binary black hole system in the blazar AO 0235+164