The OH (1720 MHz) Supernova Remnant Masers in W28: MERLIN and VLBA Polarization Observations

Abstract

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 (|B| \approx 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 to 350 mas (225 to 875 AU) with compact cores 20 mas (50 AU) in size, consistent with theoretical expectation and previous observations.

arXiv commentAASTeX, 50 pages, 16 figures (four bitmapped for arXiv), 8 tables; accepted to ApJ

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Cited by in corpus (24)

• Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W28 (G6.4-0.1) field
• A Survey of Hydroxyl Toward Supernova Remnants: Evidence for Extended 1720 MHz Maser Emission
• The Supernova Remnant W44: confirmations and challenges for cosmic-ray acceleration
• The supernova remnant W44: a case of cosmic-Ray reacceleration
• Detection of Class I Methanol (CH3OH) Maser Candidates in Supernova Remnants
• OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between the W51C Supernova Remnant and the W51B Star Forming Region
• The OH (1720 MHz) Supernova Remnant Masers in W44: MERLIN and VLBA Polarization Observations
• Laboratory evidence for proton energization by collisionless shock surfing
• Probing MHD Shocks with high-J CO observations: W28F
• The Formaldehyde Masers in Sgr B2: Very Long Baseline Array and Very Large Array Observations
• A Very High Spectral Resolution Study of Ground-State OH Masers in W3(OH)
• High Resolution Radio Astronomy Using Very Long Baseline Interferometry
• Discovery of X-ray Emission from the Galactic Supernova Remnant G32.8-0.1 with Suzaku
• X-ray Spectroscopy of the Mixed Morphology Supernova Remnant W28 with XMM-Newton
• The Effect of Far-infrared Radiation on the Hyperfine Anomaly of the OH 18 cm Transition
• CTIO, ROSAT HRI and Chandra ACIS Observations of the Archetypical Mixed-Morphology Supernova Remnant W28 (G6.4-0.1)
• MAGMO: Polarimetry of 1720-MHz OH Masers towards Southern Star Forming Regions
• Imaging of Four Galactic Supernovae Remnants in the Mid-Infrared, and their Interaction with the Interstellar Medium
• The origin of Cosmic-Rays from SNRs: confirmations and challenges after the first direct proof
• Modelling cosmic masers in C-type shock waves -- the coexistence of Class I CH3OH and 1720 MHz OH masers
• Temperature Structure of the Pipe Nebula Studied by the Intensity Anomaly of the OH 18 cm
• Collisional Pumping of OH Masers near Supernova Remnants
• The molecular emission from old supernova remnants
• A Complete X-ray View of Supernova Remnant W28 with Einstein Probe: Spatial Distribution of Parameters and Origin of the Thermal-Composite Morphology