Polarized Maser Emission with In-source Faraday Rotation
We discuss studies of polarization in astrophysical masers with particular emphasis on the case where the Zeeman splitting is small compared to the Doppler profile, resulting in a blend of the transitions between magnetic substates. A semiclassical theory of the molecular response is derived, and co...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/aca595 |
| _version_ | 1797701291351212032 |
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| author | T. L. Tobin M. D. Gray A. J. Kemball |
| author_facet | T. L. Tobin M. D. Gray A. J. Kemball |
| author_sort | T. L. Tobin |
| collection | DOAJ |
| description | We discuss studies of polarization in astrophysical masers with particular emphasis on the case where the Zeeman splitting is small compared to the Doppler profile, resulting in a blend of the transitions between magnetic substates. A semiclassical theory of the molecular response is derived, and coupled to radiative transfer solutions for 1 and 2-beam linear masers, resulting in a set of nonlinear, algebraic equations for elements of the molecular density matrix. The new code, PRISM, implements numerical methods to compute these solutions. Using PRISM, we demonstrate a smooth transfer between this case and that of wider splitting. For a J = 1–0 system, with parameters based on the v = 1, J = 1–0 transition of SiO, we investigate the behavior of linear and circular polarization as a function of the angle between the propagation axis and the magnetic field, and with the optical depth, or saturation state, of the model. We demonstrate how solutions are modified by the presence of Faraday rotation, generated by various abundances of free electrons, and that strong Faraday rotation leads to additional angles where the Stokes Q changes sign. We compare our results to a number of previous models, from the analytical limits derived by Goldreich, Keeley, and Kwan in 1973, through computational results by W. Watson and coauthors, to the recent work by Lankhaar and Vlemmings in 2019. We find that our results are generally consistent with those of other authors given the differences in the approach and the approximations made. |
| first_indexed | 2024-03-12T04:34:16Z |
| format | Article |
| id | doaj.art-e3297d666fc84434b5844998fa71fca2 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T04:34:16Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-e3297d666fc84434b5844998fa71fca22023-09-03T09:58:13ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01943212310.3847/1538-4357/aca595Polarized Maser Emission with In-source Faraday RotationT. L. Tobin0https://orcid.org/0000-0001-8103-5499M. D. Gray1https://orcid.org/0000-0002-2094-846XA. J. Kemball2https://orcid.org/0000-0001-6233-8347Department of Astronomy, University of Michigan , 1085 S. University Avenue, Ann Arbor, MI 48109, USA ; tltobin@umich.edu; Department of Physics, University of Notre Dame , Nieuwland Science Hall, Notre Dame, IN 46556, USA; Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Champaign, IL 61801, USANational Astronomical Research Institute of Thailand, 260 Moo 4, T. Donkaew, A. Maerim, Chiangmai 50180, Thailand; Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, Alan Turing Building, University of Manchester , Manchester M13 9PL, UKDepartment of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Champaign, IL 61801, USAWe discuss studies of polarization in astrophysical masers with particular emphasis on the case where the Zeeman splitting is small compared to the Doppler profile, resulting in a blend of the transitions between magnetic substates. A semiclassical theory of the molecular response is derived, and coupled to radiative transfer solutions for 1 and 2-beam linear masers, resulting in a set of nonlinear, algebraic equations for elements of the molecular density matrix. The new code, PRISM, implements numerical methods to compute these solutions. Using PRISM, we demonstrate a smooth transfer between this case and that of wider splitting. For a J = 1–0 system, with parameters based on the v = 1, J = 1–0 transition of SiO, we investigate the behavior of linear and circular polarization as a function of the angle between the propagation axis and the magnetic field, and with the optical depth, or saturation state, of the model. We demonstrate how solutions are modified by the presence of Faraday rotation, generated by various abundances of free electrons, and that strong Faraday rotation leads to additional angles where the Stokes Q changes sign. We compare our results to a number of previous models, from the analytical limits derived by Goldreich, Keeley, and Kwan in 1973, through computational results by W. Watson and coauthors, to the recent work by Lankhaar and Vlemmings in 2019. We find that our results are generally consistent with those of other authors given the differences in the approach and the approximations made.https://doi.org/10.3847/1538-4357/aca595Astrophysical masersSilicon monoxide masersCircumstellar masersRadiative transferCircumstellar envelopesMagnetic fields |
| spellingShingle | T. L. Tobin M. D. Gray A. J. Kemball Polarized Maser Emission with In-source Faraday Rotation The Astrophysical Journal Astrophysical masers Silicon monoxide masers Circumstellar masers Radiative transfer Circumstellar envelopes Magnetic fields |
| title | Polarized Maser Emission with In-source Faraday Rotation |
| title_full | Polarized Maser Emission with In-source Faraday Rotation |
| title_fullStr | Polarized Maser Emission with In-source Faraday Rotation |
| title_full_unstemmed | Polarized Maser Emission with In-source Faraday Rotation |
| title_short | Polarized Maser Emission with In-source Faraday Rotation |
| title_sort | polarized maser emission with in source faraday rotation |
| topic | Astrophysical masers Silicon monoxide masers Circumstellar masers Radiative transfer Circumstellar envelopes Magnetic fields |
| url | https://doi.org/10.3847/1538-4357/aca595 |
| work_keys_str_mv | AT tltobin polarizedmaseremissionwithinsourcefaradayrotation AT mdgray polarizedmaseremissionwithinsourcefaradayrotation AT ajkemball polarizedmaseremissionwithinsourcefaradayrotation |