Polarization of Water Masers in the presence of Velocity and Magnetic Field Gradients

Abstract

Through polarization observations water masers are excellent probes of magnetic fields in the maser region. Magnetic field strengths, such as those in the water masers regions of the envelopes of late-type stars and star-forming regions, are typically determined using a direct relation between the field strength and the observed circular polarization. Here it is shown that velocity and magnetic field gradients along the maser have a significant effect on the field strengths obtained from circular polarization observations. Due to velocity gradients the actual magnetic field strength could be up to 100% higher than the field strength derived from the observations. Additionally, when a magnetic field gradient is present, the resulting circular polarization derived is caused predominantly by the average magnetic field in the unsaturated maser core. Measurements of the fractional linear polarization are not affected by velocity or magnetic field strength gradients, though changes in the magnetic field angle along the maser do quench the linear polarization intensity when the maser saturates.

6 pages, 4 figures; accepted for publication in A&A

References in corpus (4)

• Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars
• The magnetic field around late-type stars revealed by the circumstellar H2O masers
• Probing the Magnetic Field at Sub-Parsec Radii in the Accretion Disk of NGC 4258
• Astrophysical water masers: Line profiles analysis

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• A Review of Maser Polarization and Magnetic Fields
• Measuring Magnetic Fields from Water Masers in the Synchrotron Protostellar Jet in W3(H${}_2$O)
• Intrinsic properties of the magnetically collimated water maser jet of W43A