Twenty years of blazar monitoring with the INAF radio telescopes

Abstract

The extreme variability of blazars, in both timescale and amplitude, is generally explained as the effect of a relativistic jet closely aligned to the observer's line-of-sight. Due to causality arguments, variability characteristics translate into spatial information about the emitting region of blazars. Since radiation at different wavelengths is emitted in different parts of the jet, multi-frequency observations provide us with a virtual view of the structure of the jet on different scales. Radio--gamma-ray correlations, moreover, are essential to reveal where and how the high-energy radiation is produced. We present here the observations collected within the blazar radio monitoring program that we are running at the Medicina and Noto telescopes. It aims at investigating how the variability characteristics and spectral energy distribution of blazars evolve in time. Since 2004, observation have been performed at 5, 8, 24, and 43 GHz on 47 targets, with monthly cadence; the monitoring program is still active at frequencies of 8 and 24 GHz. The database we built in more than twenty years of activity comprises to date about 21000 flux density measurements. Some basic analysis tools have been applied to the data to characterise the detected variability and offer a first glance at the wealth of information that such a program can provide about blazars.

17 pages, 6 figures, 5 tables. Accepted for publication in Astronomy & Astrophysics

References in corpus (14)

• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• The 5th edition of the Roma-BZCAT. A short presentation
• A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279
• Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006-2007
• Statistical analyses of long-term variability of AGN at high radio frequencies
• F-GAMMA: Variability Doppler factors of blazars from multiwavelength monitoring
• Multi-frequency monitoring of gamma-ray loud blazars: I. Light curves and spectral energy distributions
• The complex variability of blazars: Time-scales and periodicity analysis in S4 0954+65
• F-GAMMA: Multi-frequency radio monitoring of Fermi blazars. The 2.64 to 43 GHz Effelsberg light curves from 2007-2015
• Bimodal radio variability in OVRO-40m-monitored blazars
• Multi-messenger characterization of Mrk 501 during historically low X-ray and $\gamma$-ray activity
• Performance and first measurements of the MAGIC Stellar Intensity Interferometer
• A wiggling filamentary jet at the origin of the blazar multi-wavelength behaviour
• A flat-spectrum flare in S4 0444+63 revealed by a new implementation of multi-wavelength single-dish observations