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 milliarcseconds (mas) and VLBA data with a resolution of 15 mas, the masers are measured to have deconvolved angular sizes of 50 to 350 mas (150 to 1000 AU) with compact cores 20 mas (60 AU) in size, consistent with theoretical expectation and previous observations.