M. Villata, et al.,
Astronomy & Astrophysics, 453, 817 (2006)
Context. The radio quasar 3C 454.3 underwent an exceptional optical
outburst lasting more than 1 year and culminating in spring 2005. The
maximum brightness detected was R = 12.0, which should represent
the most lumiinous quasar state ever observed (MB ~ -31.4).
Aims. In order to follow the emission behavior of the source in detail,
a huge multiwavelength campaign was organized by the Whole Earth Blazar
Telescope (WEBT).
Methods. Continuous optical, near-IR, and radio monitoring was performed
in several bands. Moreover, ToO pointings by the Chandra and INTEGRAL
satellites provided information at high energies in May 2005.
Results. The colour-index behaviour (generally redder-when-brighter)
during the outburst suggests the presence of a luminous accretion
disc. The historical radio and optical light curves reveal a sort of
anti-correlation. Up to about 2001.0 only moderate variability
characterized the optical regime, while prominent and long-standing
radio outbursts are visible at the various radio frequency ones.
After that date, the optical activity increases and the radio flux
becomes less variable. This suggests that the two corresponding
jet emitting regions are separated and misaligned, with the inner
optical one acquiring a smaller viewing angle during the 2004-2005
outburst. A huge mm outburst has followed the opticall one, peaking
in June - July. In the meantime, the high-frequency (37 - 43 GHz)
radio flux started to increase and reached a maximum at the end of
our observing period (end of September). VLBA observations at
43 GHz during the summer strictly confirm the brightening of the
radio core and show an increasing polarization. An exceptionally
bright X-ray state was detected in May, thus correlating with the
rising mm flux and suggesting an inverse-Compton nature of the
hard X-ray spectrum.
Conclusions. A further multifrequency monitoring effort is needed
to follow the next phases of this unprecedented event.