The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI
We review results from the POLAMI program, which monitors the polarization properties of 36 blazars at the IRAM 30 m telescope. We found that the variability of the degree of linear polarization is faster and of higher amplitude at 1 mm than at 3 mm and that the linear polarization is also more vari...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-08-01
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| Series: | Galaxies |
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| Online Access: | https://www.mdpi.com/2075-4434/10/4/87 |
| _version_ | 1797432202062987264 |
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| author | Iván Agudo Clemens Thum |
| author_facet | Iván Agudo Clemens Thum |
| author_sort | Iván Agudo |
| collection | DOAJ |
| description | We review results from the POLAMI program, which monitors the polarization properties of 36 blazars at the IRAM 30 m telescope. We found that the variability of the degree of linear polarization is faster and of higher amplitude at 1 mm than at 3 mm and that the linear polarization is also more variable than the total flux. The linear polarization angle is highly variable in all sources with excursions > 180°; and for the case of the polarization angle, also the 1 mm variations appear to be faster than those at 3 mm. These results are fully compatible with recent multi-zone turbulent jet models, and they definitively rule out the popular single-zone models for blazars. They also further confirm that the short-wavelength (inner) emitting regions have better ordered magnetic fields than the long-wavelength ones (further downstream). Moreover, the POLAMI program has shown statistical evidence that, for most of the monitored sources, circular polarization emission is displayed the majority of the time. The circular polarization detection rate and the maximum degree of circular polarization found are comparable with previous surveys at much longer wavelengths, thus, opening a new window for circular polarization and jet composition studies in the mm range. The process generating circular polarization must not be strongly wavelength-dependent. The widespread presence of circular polarization in the POLAMI sample is likely due to Faraday conversion of the linearly polarized synchrotron radiation in the helical magnetic field of the jets. The peculiar behavior of circular polarization in 3C 66A, which we consider a hallmark of circular polarization generation by Faraday conversion in helical fields, is discussed. |
| first_indexed | 2024-03-09T09:56:53Z |
| format | Article |
| id | doaj.art-ff8e9411d1f8495c8035ef7624d2adad |
| institution | Directory Open Access Journal |
| issn | 2075-4434 |
| language | English |
| last_indexed | 2024-03-09T09:56:53Z |
| publishDate | 2022-08-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Galaxies |
| spelling | doaj.art-ff8e9411d1f8495c8035ef7624d2adad2023-12-01T23:43:26ZengMDPI AGGalaxies2075-44342022-08-011048710.3390/galaxies10040087The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMIIván Agudo0Clemens Thum1Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía, E-18008 Granada, SpainInstituto de Radio Astronomía Milimétrica, Avenida Divina Pastora, 7, Local 20, E-18012 Granada, SpainWe review results from the POLAMI program, which monitors the polarization properties of 36 blazars at the IRAM 30 m telescope. We found that the variability of the degree of linear polarization is faster and of higher amplitude at 1 mm than at 3 mm and that the linear polarization is also more variable than the total flux. The linear polarization angle is highly variable in all sources with excursions > 180°; and for the case of the polarization angle, also the 1 mm variations appear to be faster than those at 3 mm. These results are fully compatible with recent multi-zone turbulent jet models, and they definitively rule out the popular single-zone models for blazars. They also further confirm that the short-wavelength (inner) emitting regions have better ordered magnetic fields than the long-wavelength ones (further downstream). Moreover, the POLAMI program has shown statistical evidence that, for most of the monitored sources, circular polarization emission is displayed the majority of the time. The circular polarization detection rate and the maximum degree of circular polarization found are comparable with previous surveys at much longer wavelengths, thus, opening a new window for circular polarization and jet composition studies in the mm range. The process generating circular polarization must not be strongly wavelength-dependent. The widespread presence of circular polarization in the POLAMI sample is likely due to Faraday conversion of the linearly polarized synchrotron radiation in the helical magnetic field of the jets. The peculiar behavior of circular polarization in 3C 66A, which we consider a hallmark of circular polarization generation by Faraday conversion in helical fields, is discussed.https://www.mdpi.com/2075-4434/10/4/87galaxies: activegalaxies: jetsquasars: generalBL Lacertae objects: generalpolarizationsurveys |
| spellingShingle | Iván Agudo Clemens Thum The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI Galaxies galaxies: active galaxies: jets quasars: general BL Lacertae objects: general polarization surveys |
| title | The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI |
| title_full | The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI |
| title_fullStr | The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI |
| title_full_unstemmed | The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI |
| title_short | The Polarized Emission of AGN at Millimeter Wavelengths as Seen by POLAMI |
| title_sort | polarized emission of agn at millimeter wavelengths as seen by polami |
| topic | galaxies: active galaxies: jets quasars: general BL Lacertae objects: general polarization surveys |
| url | https://www.mdpi.com/2075-4434/10/4/87 |
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