OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between the W51C Supernova Remnant and the W51B Star Forming Region

Abstract

We present a comprehensive view of the W51B HII region complex and the W51C supernova remnant (SNR) using new radio observations from the VLA, VLBA, MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT, ASCA, and Chandra. Our VLA data include the first 400 cm (74 MHz) continuum image of W51 at high resolution (88 arcsec). The 400 cm image shows non-thermal emission surrounding the G49.2-0.3 HII region, and a compact source of non-thermal emission (W51B_NT) coincident with the previously-identified OH (1720 MHz) maser spots, non-thermal 21 and 90 cm emission, and a hard X-ray source. W51B_NT falls within the region of high likelihood for the position of TeV gamma-ray emission. Using the VLBA three OH (1720 MHz) maser spots are detected in the vicinity of W51B_NT with sizes of 60 to 300 AU and Zeeman effect magnetic field strengths of 1.5 to 2.2 mG. The multiwavelength data demonstrate that the northern end of the W51B HII region complex has been partly enveloped by the advancing W51C SNR and this interaction explains the presence of W51B_NT and the OH masers. This interaction also appears in the thermal molecular gas which partially encircles W51B_NT and exhibits narrow pre-shock (DeltaV 5 km/s) and broad post-shock (DeltaV 20 km/s) velocity components. RADEX radiative transfer modeling of these two components yield physical conditions consistent with the passage of a non-dissociative C-type shock. Confirmation of the W51B/W51C interaction provides additional evidence in favor of this region being one of the best candidates for hadronic particle acceleration known thus far.

Accepted to ApJ

References in corpus (5)

• A Survey of Hydroxyl Toward Supernova Remnants: Evidence for Extended 1720 MHz Maser Emission
• Discovery of New Interacting Supernova Remnants in the Inner Galaxy
• Very Large Array Observations of Galactic Center OH 1720 MHz Masers in Sagittarius A East and in the Circumnuclear Disk
• 74 MHz Discrete HII Absorption Regions Towards The Inner Galaxy
• A search for OH 6 GHz maser emission towards supernova remnants

Cited by in corpus (26)

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• The dense gas mass fraction in the W51 cloud and its protoclusters
• The turbulent destruction of clouds - III. Three dimensional adiabatic shock-cloud simulations
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• Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA): Inner Galaxy Data Release
• Supernova Shocks in Molecular Clouds: Velocity Distribution of Molecular Hydrogen
• Kinematic distance study of the planetary nebulae-supernova remnant-HII region complex at G35.6-0.5
• NH${}_3$(3,3) and CH${}_3$OH near Supernova Remnants: GBT and VLA Observations
• Evidence of a Hadronic Origin for the TeV Source J1834-087
• Localized SiO emission triggered by the passage of the W51C SNR shock
• Near-infrared spectroscopy of the massive stellar population of W51: evidence for multi-seeded star formation
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• Disentangling the radio emission of the supernova remnant W51C
• MAGMO: Polarimetry of 1720-MHz OH Masers towards Southern Star Forming Regions
• An XMM-Newton Study of the Mixed-Morphology Supernova Remnant G346.6-0.2
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• QUIJOTE scientific results -- V. The microwave intensity and polarisation spectra of the Galactic regions W49, W51 and IC443
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