Letter to the Editor

Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007^*

¹ INAF, Osservatorio Astronomico di Torino, Italy e-mail: villata@oato.inaf.it
² Astronomical Institute, St.-Petersburg State University, Russia
³ Pulkovo Observatory, Russia
⁴ Abastumani Astrophysical Observatory, Georgia
⁵ Astrophysikalisches Institut Potsdam, Germany
⁶ Landessternwarte Heidelberg-Königstuhl, Germany
⁷ Tuorla Observatory, University of Turku, Finland
⁸ Department of Astronomy, University of Michigan, MI, USA
⁹ Metsähovi Radio Obs., Helsinki Univ. of Tech. TKK, Finland
¹⁰ Radio Astronomy Lab. of Crimean Astrophysical Obs., Ukraine
¹¹ Max-Planck-Institut für Radioastronomie, Germany
¹² Circolo Astrofili Talmassons, Italy
¹³ SARA Observatory, Florida International University, FL, USA
¹⁴ INAF, Osservatorio Astrofisico di Catania, Italy
¹⁵ Astrophys. Inst., Dept. of Phys. & Astron., Ohio Univ., OH, USA
¹⁶ Oss. Astronomico della Regione Autonoma Valle d'Aosta, Italy
¹⁷ Armenzano Astronomical Observatory, Italy
¹⁸ Instituto de Astrofísica de Andalucía, CSIC, Spain
¹⁹ INAF, Osservatorio Astronomico di Roma, Italy
²⁰ INAF, Osservatorio Astronomico di Teramo, Italy
²¹ Agrupació Astronòmica de Sabadell, Spain
²² Instituto de Astronomía, UNAM, Mexico
²³ INAF, Istituto di Radioastronomia Sezione di Noto, Italy
²⁴ INAF, IASF-Roma, Italy
²⁵ INAF, IASF-Milano, Italy

Received: 11 February 2008
Accepted: 15 February 2008

Abstract

Aims. Since the CGRO operation in 1991–2000, one of the primary unresolved questions about the blazar γ-ray emission has been its possible correlation with the low-energy (in particular optical) emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the γ-ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong γ-ray detection of 0716+714 by AGILE.

Methods. We present the GASP-WEBT optical and radio light curves of this blazar obtained in July–November 2007, about various AGILE pointings at the source. We construct NIR-to-UV spectral energy distributions (SEDs), by assembling GASP-WEBT data together with UV data from the Swift ToO observations of late October.

Results. We observe a contemporaneous optical-radio outburst, which is a rare and interesting phenomenon in blazars. The shape of the SEDs during the outburst appears peculiarly wavy because of an optical excess and a UV drop-and-rise. The optical light curve is well sampled during the AGILE pointings, showing prominent and sharp flares. A future cross-correlation analysis of the optical and AGILE data will shed light on the expected relationship between these flares and the γ-ray events.