Water maser polarization of the water fountains IRAS 15445-5449 and IRAS 18043-2116

Abstract

We present the morphology and linear polarization of the 22-GHz water (H2O) masers in the high-velocity outflow of two post-asymptotic giant branch sources, d46 (IRAS 15445-5449) and b292 (IRAS 18043-2116). The observations were performed using the Australia Telescope Compact Array. Different levels of saturated maser emission have been detected for both sources. We also present the mid-infrared image of d46 overlaid with the distribution of the maser features that we have observed in the redshifted lobe of the bipolar structure. The relative position of the observed masers and a previous radio continuum observation suggest that the continuum is produced along the blueshifted lobe of the jet. It is likely due to synchrotron radiation, implying the presence of a strong magnetic field in the jet. The fractional polarization levels measured for the maser features of d46 indicate that the polarization vectors are tracing the poloidal component of the magnetic field in the emitting region. For the H2O masers of b292, we have measured low levels of fractional linear polarization. The linear polarization in the H2O maser region of this source likely indicates a dominant toroidal or poloidal magnetic field component. Since circular polarization was not detected, it is not possible to determine the magnetic field strength. However, we present a 3σ evaluation of the upper limit intensity of the magnetic field in the maser-emitting regions of both observed sources. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.