Infrared polarisation of blazar 3C454.3 in flare

The blazar 3C454.3 underwent a flaring episode in July 2007 during which it was detected in high energy gamma-rays by AGILE. We report on infrared polarimetric observations taken a few days after the last AGILE observation. The source was still in flare with a near-infrared flux more than ten times brighter than during quiescence periods. The infrared light was significantly polarised at the level of a few percent, comparable to previous measurements from radio to optical. No variability is detected on hour timescales but the polarisation amplitude changed from 5.3% to 2.7% between two consecutive nights without the flux or the polarisation angle changing much. Much remains to be done to characterize visible light polarisation variability in blazars and link it to the multiwavelength behaviour, notably in radio.