Far‐Infrared Polarization of the Quasar 3C 279

Abstract

We present the first far-infrared (FIR) polarization results of the OVV quasar 3C 279 obtained with ISOPHOT for two epochs in 1996 and 1997. We describe its integral polarization properties at a wavelength of 170 mu m, where the source shows a maximum in its energy distribution. After a gamma-ray flare in 1996 January, a polarization of 23% closely aligned with the radio jet axis was measured in 1996 July. In 1997 June, the polarization degree had decreased to 6.5%, with a less good alignment. On the other hand, the total 170 mu m flux is the same for both epochs. Our measurements provide additional constraints for the multiwavelength properties of synchrotron emission in radio jets and the temporal evolution of these properties: they show that the FIR radiation of 3C 279 is optically thin and that its origin is very close to the core. The variability of the FIR polarization without any change of the total FIR flux can be explained by a disordering of the magnetic field in between the core and the first stationary VLBI radio knot.