Letter to the Editor

INTEGRAL observations of the blazar 3C 454.3 in outburst

¹ INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy e-mail: pian@oats.inaf.it
² INAF, IASF-Bologna, via Gobetti 101, 40129 Bologna, Italy
³ NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA
⁴ Joint Center for Astrophysics, Department of Physics, University of Maryland, Baltimore County, MD 21250, USA
⁵ INTEGRAL Science Data Center, Chemin d'Écogia 16, 1290 Versoix, Switzerland
⁶ Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
⁷ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁸ ASI Science Data Center, via Galileo Galilei, 00044 Frascati, Italy
⁹ INAF, Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
¹⁰ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
¹¹ INAF, Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy
¹² Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
¹³ Dipartimento di Fisica, University of Perugia, via A. Pascoli, 06123 Perugia, Italy
¹⁴ Dipartimento di Fisica e Matematica, University of Insubria, via Valleggio 11, 22100 Como, Italy
¹⁵ ESA-ESTEC, RSSD, Keplerlaan 1, Postbus 299, 2200 AG Noordwijk, The Netherlands
¹⁶ Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondrejov, Czech Republic

Received: 23 December 2005
Accepted: 12 February 2006

Abstract

In Spring 2005, the blazar 3C 454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL  observations, accomplished in 15-18 May 2005. The source was detected by the INTEGRAL instruments from 3 to 200 keV in a bright state ( erg s^-1 cm^-2), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ~20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region.