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We present and analyse the WEBT multifrequency observations of 3C 454.3 inthe 2007-2008 observing season, including XMM-Newton observations and near-IRspectroscopic monitoring, and compare the recent emission behaviour with thepast one. In the optical band we observed a multi-peak outburst in July-August2007, and other faster events in November 2007 - February 2008. During theseoutburst phases, several episodes of intranight variability were detected. A mmoutburst was observed starting from mid 2007, whose rising phase wascontemporaneous to the optical brightening. A slower flux increase alsoaffected the higher radio frequencies, the flux enhancement disappearing below8 GHz. The analysis of the optical-radio correlation and time delays, as wellas the behaviour of the mm light curve, confirm our previous predictions,suggesting that changes in the jet orientation likely occurred in the last fewyears. The historical multiwavelength behaviour indicates that a significantvariation in the viewing angle may have happened around year 2000. Colouranalysis reveals a complex spectral behaviour, which is due to the interplay ofdifferent emission components. All the near-IR spectra show a prominent Halphaemission line, whose flux appears nearly constant. The analysis of theXMM-Newton data indicates a correlation between the UV excess and thesoft-X-ray excess, which may represent the head and the tail of the big bluebump, respectively. The X-ray flux correlates with the optical flux, suggestingthat in the inverse-Compton process either the seed photons are synchrotronphotons at IR-optical frequencies or the relativistic electrons are those thatproduce the optical synchrotron emission. The X-ray radiation would thus beproduced in the jet region from where the IR-optical emission comes.

A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008