Magnetic Field Morphology of Orion-IRc2 from 86 GHz SiO Maser Polarization Images

Abstract

In an attempt to probe the magnetic field morphology near the massive young star Orion-IRc2, we mapped the linear polarization of its J=2-1 SiO masers, in both the v=0 and v=1 vibrational levels, with 0.5 arcsec resolution. The intense v=1 masers are confined to a narrow zone 40 AU from the star. Their polarization position angles vary significantly on time scales of years. For the v=1 masers the stimulated emission rate R is likely to exceed the Zeeman splitting gΩdue to any plausible magnetic field; in this case the maser polarization need not correlate with the field direction. The much weaker v=0 masers in the ground vibrational level lie 100-700 AU from IRc2, in what appears to be a flared disk. Their fractional polarizations are as high as 50%. The polarization position angles vary little across the line profile or the emission region, and appear to be stable in time. The position angle, P.A. = 80 degrees, we measure for the J=2-1 masers differs by 70 degrees from that measured for the J=1-0 SiO transition, possibly because of Faraday rotation in the foreground, Orion A, HII region. A rotation measure RM = 3.3 \times 10^4 rad m${}^{-2}$ is required to bring the J=2-1 and J=1-0 position angles into concordance. The intrinsic polarization position angle for both transitions is then 57 degrees, parallel to the plane of the putative disk. Probably the magnetic field threads the disk poloidally. There is little evidence for a pinched or twisted field near the star.

arXiv commentaccepted for publication in ApJ

References in corpus (2)

• High Resolution Millimeter-Wave Mapping of Linearly Polarized Dust Emission: Magnetic Field Structure in Orion
• Coexisting conical bipolar and equatorial outflows from a high-mass protostar

Cited by in corpus (14)

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• The ALMA View of the OMC1 Explosion in Orion
• A line confusion limited millimeter survey of Orion KL. II: Silicon-bearing species
• Full polarization study of SiO masers at 86 GHz
• Multi-epoch imaging polarimetry of the SiO masers in the extended atmosphere of the Mira variable TX Cam
• Hubble Space Telescope NICMOS Polarization Measurements of OMC-1
• ALMA Images of the Orion Hot Core at 349 GHz
• Characterizing the accuracy of ALMA linear-polarization mosaics
• Polarization morphology of SiO masers in the circumstellar envelope of the AGB star R Cassiopeiae
• A Review of Maser Polarization and Magnetic Fields
• Characterizing maser polarization: effects of saturation, anisotropic pumping and hyperfine structure
• Magnetic Field Structure of Orion Source I