Multi-frequency monitoring of γ-ray loud blazars

I. Light curves and spectral energy distributions

¹ INAF – Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy e-mail: ubach@mpifr-bonn.mpg.de
² Osservatorio Astronomico, Università di Perugia, via B. Bonfigli, 06126 Perugia, Italy
³ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁴ Astronomical Institute, St. Petersburg State University, Universitetsky pr. 28, Petrodvoretz, 198504 St. Petersburg, Russia
⁵ INAF – Istituto di Radioastronomia, Sezione di Noto, C.da Renna Bassa – Loc. Case di Mezzo C.P. 141, 96017 Noto, Italy
⁶ Pulkovo Astronomical Observatory of the Russian Academy of Sciences, Russia
⁷ Agrupació Astronòmica de Sabadell, PO Box 50, 08200 Sabadell, Spain
⁸ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁹ INAF – Osservatorio Astronomico di Collurania Teramo, via Maggini snc, 64100 Teramo, Italy
¹⁰ Ulugh Beg Astronomical Institute, 33 Astronomical Str., Tashkent 700052, Uzbekistan
¹¹ Abastumani Astrophysical Observatory, 383762 Abastumani, Georgia
¹² INAF – Istituto di Radioastronomia, Sezione di Medicina, via Fiorentina 3508/B, 40059 Medicina, Italy

Received: 13 October 2006
Accepted: 14 November 2006

Abstract

Context.Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei.

Aims.Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites.

Methods.Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised.

Results.Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.