TY - JOUR
T1 - Hints of high core Faraday rotations from a joint analysis of VLBA and optical polarization data
AU - Algaba, Juan Carlos
AU - Gabuzda, Denise C.
AU - Smith, Paul S.
N1 - Publisher Copyright:
© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
PY - 2008
Y1 - 2008
N2 - Although the continua of radio-loud Active Galactic Nuclei (AGN) are typically dominated by synchrotron radiation over virtually the entire spectrum, it is not clear whether the radio and higher-frequency emission originate in the same or different parts of the jet. Several different radio-optical correlations based on polarization data have been found recently, suggesting that the optical and radio polarization may be closely related, and that the corresponding emission regions may be cospatial[3, 6, 2]. Our joint analysis of optical and VLBA polarization data for a sample of about 40 AGNs shows that, after correction for the inferred VLBA core Faraday rotations, most BL Lac objects and some quasars have aligned VLBA-core and optical polarizations, although many quasars also show no obvious relationship between their VLBA-core and optical polarization angles. This may indicate that not all AGNs have cospatial regions of optical and radio emission in their jets. However, another possibility is that some of the 7mm-2cm VLBA cores have Faraday rotations of the order of several tens of thousand of rad/m2, which were not properly fit by our three-frequency data due to nπ ambiguities in the observed polarization angles, leading to incorrect subtraction of the effects of the core Faraday rotation, and so incorrect “zero-wavelength” radio polarization angles. The possibility of such high core Faraday rotations is supported by the results of the parsec-scale Faraday-rotation studies of Zavala & Taylor[11] and Jorstad et al.[6].
AB - Although the continua of radio-loud Active Galactic Nuclei (AGN) are typically dominated by synchrotron radiation over virtually the entire spectrum, it is not clear whether the radio and higher-frequency emission originate in the same or different parts of the jet. Several different radio-optical correlations based on polarization data have been found recently, suggesting that the optical and radio polarization may be closely related, and that the corresponding emission regions may be cospatial[3, 6, 2]. Our joint analysis of optical and VLBA polarization data for a sample of about 40 AGNs shows that, after correction for the inferred VLBA core Faraday rotations, most BL Lac objects and some quasars have aligned VLBA-core and optical polarizations, although many quasars also show no obvious relationship between their VLBA-core and optical polarization angles. This may indicate that not all AGNs have cospatial regions of optical and radio emission in their jets. However, another possibility is that some of the 7mm-2cm VLBA cores have Faraday rotations of the order of several tens of thousand of rad/m2, which were not properly fit by our three-frequency data due to nπ ambiguities in the observed polarization angles, leading to incorrect subtraction of the effects of the core Faraday rotation, and so incorrect “zero-wavelength” radio polarization angles. The possibility of such high core Faraday rotations is supported by the results of the parsec-scale Faraday-rotation studies of Zavala & Taylor[11] and Jorstad et al.[6].
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M3 - Conference article
AN - SCOPUS:85055576889
SN - 1824-8039
VL - 72
JO - Proceedings of Science
JF - Proceedings of Science
M1 - 006
T2 - 9th European VLBI Network Symposium on The role of VLBI in the Golden Age for Radio Astronomy and EVN Users Meeting, EVN Symposium 2008
Y2 - 23 September 2008 through 26 September 2008
ER -