2004/10/24 by Ian M. Hoffman, W. M. Goss, C. L. Brogan +1 · 3 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Astrophysics and Star Formation Studies #Ionosphere and magnetosphere dynamics #astro-ph
paper · pdf · doi:10.1086/427018
published as Astrophys.J. 620 (2005) 257-273 · AASTeX, 50 pages, 16 figures (four bitmapped for arXiv), 8 tables; accepted to ApJ
arxiv created 2004/10/24 · openalex publication_date 2005/02/09 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Full-polarization MERLIN and VLBA observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant W28 are presented. Zeeman splitting (| | ≈ 0.75 mG) has been directly resolved between right- and left-circularly polarized spectra for the first time. Linear polarization position angles and circular polarization Zeeman splitting observed in the maser emission permit interpretation of a comprehensive picture of the magnetic field at the supernova/molecular cloud interface marked by the masers. We find the post-SNR shock magnetic field to be well ordered over the ~1 pc covered by the maser region (compared with the approximately 30 pc diameter of the entire SNR) and well aligned with the shock front that is traced by synchrotron radiation and molecular emission. 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 90-350 mas (225-875 AU) with compact cores 20 mas (50 AU) in size, consistent with theoretical expectation and previous observations.