Letter to the Editor

The GASP-WEBT monitoring of 3C 454.3 during the 2008 optical-to-radio and γ-ray outburst ^*

¹ INAF - Osservatorio Astronomico di Torino, Italy
² Harvard-Smithsonian Center for Astrophysics, MA, USA
³ Astronomical Institute, St.-Petersburg State University, Russia
⁴ Pulkovo Observatory, Russia
⁵ Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
⁶ Abastumani Astrophysical Observatory, Georgia
⁷ Department of Astronomy, University of Michigan, MI, USA
⁸ Metsähovi Radio Observatory, Helsinki University of Technology TKK, Finland
⁹ Institute of Astronomy, National Central University, Taiwan
¹⁰ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Finland
¹¹ Instituto de Astrofísica de Andalucía, CSIC, Spain
¹² Max-Planck-Institut für Radioastronomie, Germany
¹³ Institute of Astronomy, Bulgarian Academy of Sciences, Bulgaria
¹⁴ Circolo Astrofili Talmassons, Italy
¹⁵ Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico
¹⁶ INAF - Osservatorio Astrofisico di Catania, Italy
¹⁷ Astrophysical Institute, Department of Physics and Astronomy, Ohio University, OH, USA
¹⁸ Osservatorio Astronomico della Regione Autonoma Valle d'Aosta, Italy
¹⁹ Armenzano Astronomical Observatory, Italy
²⁰ INAF - Osservatorio Astronomico di Roma, Italy
²¹ INAF - Osservatorio Astronomico di Collurania Teramo, Italy
²² Agrupació Astronòmica de Sabadell, Spain
²³ ZAH, Landessternwarte Heidelberg-Königstuhl, Germany
²⁴ Institute for Astrophysical Research, Boston University, MA, USA
²⁵ INAOE, Mexico
²⁶ Department of Physics, University of Colorado Denver, CO, USA

Received: 19 June 2009
Accepted: 12 August 2009

Abstract

Context. Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in the brightest optical state ever observed, during the 2004-2005 outburst. The Whole Earth Blazar Telescope (WEBT) consortium has carried out several multifrequency campaigns to follow the source behaviour.

Aims. The GLAST-AGILE Support Program (GASP) was born from the WEBT to provide long-term continuous optical-to-radio monitoring of a sample of γ-loud blazars, during the operation of the AGILE and GLAST (now known as Fermi GST) γ-ray satellites. The main aim is to shed light on the mechanisms producing the high-energy radiation, through correlation analysis with the low-energy emission. Thus, since 2008 the monitoring task on 3C 454.3 passed from the WEBT to the GASP, while both AGILE and Fermi detected strong γ-ray emission from the source.

Methods. We present the main results obtained by the GASP at optical, mm, and radio frequencies in the 2008-2009 season, and compare them with the WEBT results from previous years.

Results. An optical outburst was observed to peak in mid July 2008, when Fermi detected the brightest γ-ray levels. A contemporaneous mm outburst maintained its brightness for a longer time, until the cm emission also reached the maximum levels. The behaviour compared in the three bands suggests that the variable relative brightness of the different-frequency outbursts may be due to the changing orientation of a curved inhomogeneous jet. The optical light curve is very well sampled during the entire season, which is also well covered by the various AGILE and Fermi observing periods. The relevant cross-correlation studies will be very important in constraining high-energy emission models.