The OH (1720 MHz) Supernova Remnant Masers in W44: MERLIN and VLBA Polarization Observations

Full-polarization MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant W44 are presented. Zeeman splitting has been directly resolved between right- and left-circularly polarized spectra indicating magnetic field strengths of "B" - 0.50 mG. The position angle of the linear polarization is in good agreement with the orientation of the shocked gas at the supernova remnant/molecular cloud interface. Based on MERLIN data having a resolution of 200 mas and VLBA data with a resolution of 15 mas, the masers are measured to have deconvolved angular sizes of 50-350 mas (150-1000 AU) with compact cores 20 mas (60 AU) in size, consistent with theoretical expectation and previous observations.