Fast variability and circular polarization of the 6.7 GHz methanol maser in G33.641$-$0.228
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arXiv
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| Main Authors: | , , , , , , , |
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| Format: | Preprint |
| Published: |
2026
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| _version_ | 1866915763424591872 |
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| author | Fujisawa, Kenta Sugiura, Yui Kojima, Yuta Sugiyama, Koichiro Niinuma, Kotaro Motogi, Kazuhito Tanabe, Yoshihiro Yonekura, Yoshinori |
| author_facet | Fujisawa, Kenta Sugiura, Yui Kojima, Yuta Sugiyama, Koichiro Niinuma, Kotaro Motogi, Kazuhito Tanabe, Yoshihiro Yonekura, Yoshinori |
| contents | The 6.7 GHz methanol maser in a high-mass star-forming region G33.641$-$0.228 is known to exhibit burst-like flux variability due to an unknown mechanism. To investigate the burst mechanism, we conducted high-cadence flux and circular polarization monitoring observations, simultaneously using left- and right-hand circular polarizations. We found that the flux density increased and decreased on a short timescale of 0.3 d during a burst. We also found strong circular polarization, reaching up to 20\% in the component exhibiting the bursts. Circular polarization of 0--20\% was continuously observed from 2009 to 2016, even in the quiescent period. The polarization also varied on timescales of less than one day. When a burst occurred and the flux density increased, the circular polarization decreased to zero. To explain the observational properties of the flux variability and circular polarization, we propose a model in which an explosive event similar to a solar radio burst occurs on the line of sight behind the maser cloud, producing circularly polarized continuum emission due to gyro-synchrotron or gyro-resonance radiation, which is then amplified by the maser. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_20371 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Fast variability and circular polarization of the 6.7 GHz methanol maser in G33.641$-$0.228 Fujisawa, Kenta Sugiura, Yui Kojima, Yuta Sugiyama, Koichiro Niinuma, Kotaro Motogi, Kazuhito Tanabe, Yoshihiro Yonekura, Yoshinori Solar and Stellar Astrophysics The 6.7 GHz methanol maser in a high-mass star-forming region G33.641$-$0.228 is known to exhibit burst-like flux variability due to an unknown mechanism. To investigate the burst mechanism, we conducted high-cadence flux and circular polarization monitoring observations, simultaneously using left- and right-hand circular polarizations. We found that the flux density increased and decreased on a short timescale of 0.3 d during a burst. We also found strong circular polarization, reaching up to 20\% in the component exhibiting the bursts. Circular polarization of 0--20\% was continuously observed from 2009 to 2016, even in the quiescent period. The polarization also varied on timescales of less than one day. When a burst occurred and the flux density increased, the circular polarization decreased to zero. To explain the observational properties of the flux variability and circular polarization, we propose a model in which an explosive event similar to a solar radio burst occurs on the line of sight behind the maser cloud, producing circularly polarized continuum emission due to gyro-synchrotron or gyro-resonance radiation, which is then amplified by the maser. |
| title | Fast variability and circular polarization of the 6.7 GHz methanol maser in G33.641$-$0.228 |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2601.20371 |